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been tenanted by dwarfs, or that there was any dwarf tribe in the country. It is especially noteworthy that Du Bekr, the confidential agent of the British Government at the Court of Morocco, replied to Sir William Kirby Green that no Moor had ever heard of a race of dwarfs in the country. Sir William knew how to interrogate a Moor, and as he accepted Du Bekr's statement, I have no doubt that Du Bekr was speaking the truth. Until the existence of a race of dwarfs in the Atlas Mountains is proved, it is idle to indulge in guesses at the reasons which have led to the fact of its existence being jealously kept secret ; so I shall not follow Mr. Halliburton in the argument by which he seeks to show that the race has been regarded with superstitious reverence, and so kept apart. In all countries, at all times, I believe dwarfs and deformed persons have been looked at askance by the ignorant and superstitious. In Scotland they were regarded as fairies of a brutal and malignant type; and in Morocco I have no doubt they have been credited with the possession of the evil eye and of other pernicious powers. But to maintain that a tribe of them has ever been held sacred and worshipped in the heart of a Mahometan country that is fiercely fanatical is to do violence to our fundamental conceptions of

Islam.

Mr. Halliburton's statements about the origin and habits of his supposed tribe of dwarfs are not more worthy of discussion than his theory of the causes which have led to their concealment. They are derived from native sources of the most tainted description, and are either pure inventions, or concoctions of truth and falsehood. We are told that a tribe of acrobats—the Ait Sidi Hamed O Moussa (the tribe of the son of Moses)—is an offshoot of the Aglimien dwarfs, living between the Dra and Akka; that they are a rather small race with a light red complexion; and that dwarfs perform with them in Southern Morocco, but avoid the coast towns where Europeans are; and that they are smiths and tinkers. Now, the paragraph setting forth these statements contains just as much error and confusion as it is possible to cram into so many words. The Sidi Hamed O Moussa are not a tribe at all, but the followers of a saint whose Kuba is not far from Taradant. Their troupes are made up of men drawn from various parts of the country; and it would be as correct to regard the Jesuits as a tribe, and describe their ethnic characteristics, as it is to assign distinctive features to the Sidi Hamed O Moussa. Then, as a matter of fact, they are not unusually small men, they are not smiths and tinkers, and they never have dwarfs performing with them either in town or country. I saw several troupes of them in Southern Morocco, and can testify that they are of average size and of the usual Moorish tint; that they follow a more profitable trade than that of tinkering; and that they have no dwarfs among them.

Mr. Halliburton s'rongly advises European travellers and touris's to abstain from any attempt to enter the districts of Morocco inhabited by the dwarfish race, as they would inevitably, while doing so, be murdered or robbed, whether Moslems, Jews, or Christians. The advice is judicious, for open-mouthed travellers of any persuasion, in quest of dwarfs, are not unlikely to be murdered or robbed in any part of Morocco except in those coast towns to which Mr. Halliburton has apparently confined his own wanderings in the country. European travellers of another sort, however-resolute, incredulous men, explorers, and pioneers of trade and commerce-will certainly before long penetrate all those regions where the dwarfish race has been located by Mr. Halliburton. Remembering what I have heard on good authority of the resources of some of those regions, and the indications I have seen of the mineral wealth of that region to the south of the Atlas where Mr. Halliburton has placed the original home of his dwarfs, I feel disposed to exclaim, like the old sailor in Millais's famous picture "The North-West Passage": "It can be done, and England ought to do it!" When, however, these regions are opened up, I feel sure that, amongst much that is wonderful in them, there will be found no tribe of dwarfs hemmed in by religious sentiment.

To those interested in the generation and growth of myths in modern times, and under Congress culture, Mr. Halliburton's dwarf-story cannot but afford an instructive study.

HAROLD CRICHTON-BROWNE.

Macloustie Camp, Bechuanaland, November 15, 1891.

Sun-spots and Air-temperature.

IT is now widely believed by meteorologists that a certain relation exists between the solar sun-spot cycle and the air-tem

perature of the earth, such that to a minimum of sun-spots corresponds, approximately, a maximum of air-temperature, and vice versa. From the comprehensive researches of Dr. Köppen on the subject some time ago, it appeared that this relation is most clearly proved in the case of the tropics, the evidence becoming less as we go north and south. Mr. Blanford showed recently in NATURE (vol. xliii. p. 583) that the evidence in the case of India has of late years greatly increased in force.

In a climate so variable as ours it is not, perhaps, to be expected that the existence of such a relation should be very patent and obvious. And there may be some legitimate doubt whether its existence has yet been demonstrated. It is in the hope of possibly advancing the matter somewhat that the following facts are presented.

If we decide to take for our consideration a part of the year instead of the whole, we shall naturally select the hotter part; the part in which the solar action is greatest (just as we might expect to find, and do find, better proof of the relation in tropical than in cold countries). I select the four months June to September. The data used are, Mr. Belleville's observations of Greenwich mean temperature from 1812-1855, which are, it should be noted, reduced to sea-level (see Quart. Journ. of the R. Met. Soc., January 1888, p. 27), and thereafter the ordinary Greenwich figures. The average difference (about half a degree) does not materially affect the purpose here set.

Taking the mean temperature of those four months, and smoothing the values by means of five-year averages, we get the second, thick line curve in the upper diagram herewith. The dotted line curve is that of sun-spots, inverted (i.e. minima above and maxima below). The vertical scales for these are both to the left.

There is evidently a correspondence between these curves as far as about 1870; maxima of temperature lagging a little, as a rule, behind minima of sun-spots, and minima of temperature behind maxima of sunspots. Since about 1870, the correspondence appears to fail. We look for a temperature-maximum about 1879, and we do not find it.

A consideration of the rainfall here seems instructive. The smoothed curve of rainfall in those four months (third in the diagram; Chiswick to 1869, thereafter Greenwich) is, in the main, roughly inverse to the temperature-curve, as we might expect. Yet it is difficult to trace a very definite relation between it and the sun-spot curve. Thus, consider the three most salient "crests " in it. The first (in height as well as time), in 1829, is close before a sunspot maximum, 1830. The second (least salient of the three), in 1861, is close after a sunspot maximum, 1860. The third, in 1879 and 1880, is close after a sunspot minimum, 1878. These rainfall variations, indeed, seem to be under some different law, and it will be observed that the last crest comes (the first example in the whole period) just about where we should expect, from previous experience, to find a temperature-maximum. The regular variation of this curve in one direction for several years is a noteworthy feature recently (in 1880 to 1885, and again in 1885 to 1889). Is the curve now near a maximum which will te found to coincide with a further obliteration of the normal correspondence between sun-spots and temperature?

We have thus far considered the group of four months, and they seem to me to support the view under consideration. May we further look for the relation in individual months?

Suppose we see reason in doing so, and make a selection. The most likely month would perhaps seem to be July, as having the maximum temperature; or June, as that month in which the sun is highest.

On examining the smoothed curves of mean temperature for each of those four months, we find that June and September show a large amount of the correspondence with the sun-spot curve, while the two others do not show much correspondence. These two curves (June and September) are given in the lower diagram, superposed; the two vertical scales being at the left. June, it will be noticed, presents a wave crest fairly corresponding with each of the six, or seven, sun-spot minima. In the case of September there is a pronounced failure at the sun-spot minimum in 1878.

As a possibly good reason why September might show the relation, while July and August do not (or not so well), I would suggest the fact that September is the month with least cloud. Between May and September, cloud increases to a small secondary maximum in July.

The absence of a maximum of temperate in September

corresponding to the sun-spot minimum in 1878 may, perhaps, be connected, as in the case of the four months' curve, with the rainfall. A smoothed curve of humidity for September rises, I find, to a high maximum in 1880. The June humidity curve does the same, and if it be therefore asked, why we should not have a similar failure in that month's curve, I would invite attention to the fact that the rise to the maximum in the humidity curve for June is a rapid one from the absolute minimum (reckoning from 1858) in 1876; while the rise in September is

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predicted time, given in Marth's ephemeris (Monthly Notices, March 1891), is 5h. 32'6m., so that the spot was 10'4m. late, and this means a decided slackening in its motion of rotation during the present apparition. On August 7, 1891, I saw the spot pass the central meridian at 11h. 32m., or only 2.3m. after the time indicated in Marth's ephemeris. In the interval of 5 months, during which 362 rotations were performed, the mean period has been 9h. 55m. 42s., which is nearly 1 second greater than the rotation period of this marking as observed here during

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more gradual from an absolute minimum in 1870. Thus, the wave in June corresponding to the sun-spot minimum in 1878 might be regarded as but partially formed, the growing humidity, or rainfall, presenting its normal culmination.

However this may be (and I do not press these suggestions), it has seemed to me desirable to submit the cincidences presented in the diagram (which I have difficulty in thinking wholly fortuitous, and which are quite in harmony with the general view enunciated by Köppen) to minds more competent to estimate their nature rightly. A. B. M.

The Red Spot on Jupiter.

ON January 4 last, at 5h. 43m., the red spot on Jupiter was estimated to be on the central meridian of the planet. The

any previous opposition. In 1890 I determined the period as 9h. 55m. 40'2s., which differed very slightly from that derived from my observations in 1887, 1888, and 1889. It now appears, however, that a marked retardation has occurred, and it remains to be seen whether this will be maintained until the close of the apparition.

The spot continues to be a fairly conspicuous object, and it retains its oval outlines, but it is not nearly so dark and definite as it was in the years from 1878 to 1881. Bristol, January 10. W. F. DENNING.

The Implications of Science.

DR. MIVART complains that in my last letter I merely affirmed without arguing. This is in a measure true as, to

economize your space, I only gave the skeleton of the argument, but I hoped I had said enough to indicate at least the general outline of my logical views. But as this seems not to have been quite the case, may I now explain myself a little more fully?

I may remove a slight misunderstanding at once. I said our knowledge of our own continuous existence in the present is to each of us a necessary truth. Dr. Mivart reads this as if I had written "our continued existence in the future"! That we cannot be annihilated while we know that we are existing is, as I shall presently show, not a mere consequence of the law of contradiction. If this law is of any use at all in proving the conclusion, it would certainly be useless without a second premiss, viz. that we are existing; and this latter is the premiss which is a necessary truth.

I suppose everyone will acknowledge that a definition is essentially an arbitrary assertion, and that therefore a definition can by itself give no real information. But a well-understood term does not consist of a definition alone. Its definition may be laid down, as a list of items of connotation (or denotation), and the other part of its meaning, which may be called its import, that is its denotation (or connotation) must be discovered by experience; and the knowledge so acquired is real, not only verbal, knowledge. Now it is possible from a number of definitions alone to deduce a series of propositions. These, like the definitions from which they were deduced, give by themselves only verbal information-they are all truisms-and before they can be made of any practical use, certain real assertions, assigning real import to the terms, and so expressing real knowledge, must be added to the premisses. Thus, if we wish to determine whether any given proposition is a truism, or conveys real information, we have only to examine the definitions of its terms. If these are found to be inconsistent with each other, the proposition is a contradiction in terms, and must be rejected. If the definitions are not inconsistent, but are independent of each other, the proposition can only be intended to assert the identity of the import of its terms-it therefore conveys real information, which may either be true or false. Lastly, if the definitions can be shown to be dependent on each other, the proposition is equally true whatever import its terms may have, or even if they have no conceivable import at all. It is a truism. If, however, by the aid of other real propositions any real import can be given to its terms, it may have objective, or subjective, applications; but the objectivity or subjectivity is introduced by those other propositions, and is not a property of the original truism.

Take, for example, the proposition, "Everything must either 'be' or 'not be ""; or the proposition, "Twice two is four." The truth of either of these propositions depends solely on the definitions of its terms, as I pointed out in my last letter, and this is why I cannot regard them as objective truths. Of course

I do not doubt that if I had lost an eye I should not remain in the same condition as I was before. But, although "no man out of Bedlam would suppose a statement of a general law would inform us about a concrete thing," this is precisely what

as I prefer to call it, symbolic, reasoning. The essence of induction, in my opinion, is the assumption (at first arbitrarily) of an hypothesis to account for observed facts- that is, ultimately, of directly apprehended sensations. The full significance of the hypothesis is elucidated by symbolic reasoning, and the enumeratio simplex is applied to the results of this reasoning, and does not, therefore, appear quite in the simple form exhibited by Miss Jones. But it remains equally true that no induction can ever lead to a necessary truth.

(3) Miss Jones's view of mathematical reasoning is exactly that which I wish to combat. We do not, in mathematics, conclude a universal proposition from a single concrete instance. A mathematical formula does not imply the existence of any instance whatever of its application, any more than a definition implies the reality of the thing defined. The formula is deduced from what may logically be regarded as definitions, and one or any number of applications may indeed be found afterwards, but only by the aid of additional real premisses. It is difficult to exemplify this in the case of geometry, because the accepted geometrical methods are so very imperfect, and geometrical conclusions are not always deduced from definitions alone.

As

I implied in my former letter, some of them are founded on induction. But it must be evident that the truth of, say, De Moivre's Theorem, does not depend on our having seen that it was true in any one instance.

(4) If Miss Jones reads her own paragraph (4) again carefully, I think she will see that it is not I who have contradicted myself. I showed that if the definitions of the terms of a certain proposition were altered, the proposition might no longer be true, and that if they were not altered it would always be true. Argal, the truth depends on the definitions, and on nothing else. I did not maintain that it could ever be to anyone a necessary truth that he was writing with a lead-pencil. That would be an objective proposition, such as I was careful to insist could only be proved by induction. It might, however, be a necessary truth to anyone that he thought he was writing with a leadpencil. As to mathematical truths, so far from believing that "in as far as 'real' they are obtained by induction," I expressed my opinion that they are not "real" at all, but all truisms. Any reality in their applications must be added from outside, by real assertions which are not "mathematical." I object to calling truisms "necessary," not because they are possibly false, but because their truth is only arbitrary. On the other hand, when I call "the apprehension of a present fact" a necessary truth, I mean something more than that it is certain—namely, that its contradictory is unthinkable. EDWARD T. DIXON.

Trinity College, Cambridge, January 8.

FRESH EVIDENCE CONCERNING THE DISTRIBUTION OF ARCTIC PLANTS DURING THE GLACIAL EPOCH.

Dr. Mivart does if he regards the above proposition as depend- LA

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ent solely on the law of contradiction. Does he not see that he added the objective element to that law in the phrase, "if he had lost an eye"? "Much virtue in If." The status of the proposition, "Two straight lines cannot inclose a space,' similarly depends on the definitions of its terms; but, as I pointed out in my last letter, these terms may be defined in two different ways-either by dependent definitions, so making the proposition a truism, or independently so as to make it a real assertion, in which case it might conceivably be false. Dr. Mivart apparently takes the former set of definitions, and then implies that I deduced the latter result from them, which, if he reads my letter again, he will find not to have been the case. In reply to Miss Jones, I may point out

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(1) It most certainly is merely a verbal convention when Miss Jones says, "A and a are not applicable to the same thing.' She had herself just before laid down the convention in question, in the phrase, "If A signifies the negation of a (whatever A may stand for)."

I do not know why Miss Jones should imagine that I think that "assertions (or denials) of the existence' of particular objects are the only real propositions," but perhaps she will understand my view better when she has read this letter.

(2) I certainly hold that "inductions have no logical justification whatever," if by "logic" is to he understood formal, or,

AST summer (1891) I spent some weeks in Western Russia and Northern Germany, in order to ascertain whether the glacial fresh-water deposits of those countries contained any remains of the vegetation which lived there immediately after the inland ice had melted away. The results of my journey being favourable, I have thought it desirable to communicate them to the readers of NATURE; but before doing so it might be convenient to give a brief summary of previous investigations on the same subject.

1

The

The first discovery of fossil Arctic plants was made in England by Mr. W. Pengelly, who found in 1860, at Bovey Tracey, in Devonshire, leaves of the dwarf birch (Betula nana), together with leaves of some willows, as Salix myrtilloides, S. cinerea, S. sp. indet. leaves were identified and described by the late Prof. Heer, who pronounced the opinion that the presence of Betula nana was conclusive evidence of "a colder climate than Devonshire has at the present day." The significance of this discovery was, however, but little appreciated until the researches mentioned below again Philosophical Transactions. 1862, p. 1039 In this paper Heer mentions Salix repens (?), but this determination was subsequently altered to S. myrtilloides.

called attention to the nature of the vegetation which grew round the margin of the great northern inland ice, on the soil which was left bare when it melted away. During my first visit to Spitzbergen, in 1870, it occurred to my mind that-supposing the glacial theory were true-the remains of those Arctic plants which, in all probability, formerly existed in the area once covered by the great Scandinavian inland ice, would have been buried in the glacial fresh-water deposits, just in the same manner as the leaves of Salix polaris, Dryas octopetala, Polygonum viviparum, &c., are at the present day carried into the small lakes of Spitzbergen,

found the Arctic fossil flora underneath some peat-mosses in the immediate vicinity of Copenhagen. In 1872 I discovered leaves of Betula nana in a peat-moss near Oertzenhof, in Mecklenburg, and at Kolbermoor, in Southern Bavaria. In Switzerland I also found an Arctic-Alpine flora in a fresh-water deposit at Schwerzenbach, on the low ground between Zürich and Bodensee. The flora was rich in such species as Betula nana, Salix reticulata, S. polaris, S. retusa, S. myrtilloides, Arctostaphylos uvaursi, Polygonum viviparum, Azalea procumbens, &c. From Switzerland I went to England, and first visited Bovey Tracey (17),' where I re-found Betula nana in the

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SKETCH MAP SHOWING THE LOCALITIES WHERE ARCTIC PLANT-FOSSILS HAVE BEEN FOUND WITHIN THE AREA ONCE COVERED BY THE GREAT NORTHERN ICE-SHEET.

A, margin of the great northern inland ice at the climax of glaciation; B, margin of the Uralo-Timan glacier (according to Nikitin); c, margin of the glaciers of the Alps.

(1) Several localities (more than thirty) in Scania; (2) Rangilstorp, near Vadstena; (3) Fröjel, in the isle of Gotland; (4) several localities in Jemtland; (5) Leine, in Norway; (6) several localities in Seeland; (6) Moen; (6) Northern Jutland; (6) Bornholm; (7) Kunda, in Esthonia: (8) Samhof and Kinzli, in Livonia: (9) Pingo and Wieratz in Livonia: (10) two localities at Rjeshiza, Government of Vitebsk; (11) Kuhrische Nehrung: (12) Schroop, in Western Prussia: (13) Krampkewitz, in Pomerania; (14) Neetzka and Oertzenhof, in Mecklenburg: (15) Nantrow, in Mecklenburg; (16) Projensdorf, north of Kiel: (17) Bovey Tracey, in Devonshire; (18) Hoxne, in Suffolk; (19) several localities at and near Cremer, Norfolk; (20) Holmpton, Yorkshire; (21) Bridlington, Yorkshire; (22) localities near Edinburgh.

and buried at their bottoms. On my return from that expedition, I at once examined some glacial fresh-water deposits at Alnarp, in Scania, and was glad to find in them the leaves of Salix polaris, S. herbacea, S. reticu lata, Dryas octopetala, Betula nana, &c.; thus proving that a true Arctic flora had once lived in the southernmost part of Sweden. The next year, after having discovered the same flora in a great many other localities of the same province, I was invited by Prof. Japetus Steenstrup to extend my researches into Denmark; and our joint investigations were soon crowned with success, for we

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original locality, and also in another little basin close by, together with leaves of Arctostaphylos uva-ursi and Betula alba. Then I went to the coast of Norfolk, where I was so fortunate as to find Salix polaris and Hypnum turgescens in the pre-glacial deposits between the boulderclay and the forest-bed in the vicinity of Cromer (19). This plant-bearing bed has since then been noticed by Mr. Clement Reid, of the Geological Survey, who has named it the "Arctic fresh-water bed," and he has traced 1 The figures within parentheses refer to those on the accompanying sketch

map.

it in some other places on the coast of Norfolk. Besides Salix polaris, Mr. Reid has also found in it leaves of Betula nana and seeds of some other plants. At Hoxne, in Suffolk (18), Messrs. Reid and Ridley have discovered Salix polaris, S. myrsinites, and Betula nana, together with many other species in a glacial fresh-water deposit of a precisely similar character to those in Southern Sweden. Again, in 1879, I found leaves of Betula nana in a peat-moss at Bridlington (21), and the same plant has been found by Mr. Reid at Holmpton (20). According to a statement of Mr. Reid, Salix herbacea was found some years ago by Mr. Bennie in an inter-glacial deposit at Hailes, about three miles from Edinburgh. Finally, during this present year (1891), Mr. Reid has himself discovered a rich Arctic flora, yielding Salix polaris, S. herbacea, S. reticulata, Azalea procumbens, and Betula nana, in lacustrine deposits immediately above the boulderclay near Edinburgh (22).1

Returning to Sweden, a great many new localities yielding Arctic plants have also been found in Scania since 1871, partly by myself, partly by Dr. Gunnar Andersson and others, so that the number of localities in Scania (1) now exceeds thirty. In Ostrogothia, leaves of Betula nana and Dryas octopetala, &c., were found in 1886 in a calcareous tufa near Vadstena at Lake Vetter (2); and in the isle of Gotland (3), Mr. R. Sernander, in 1890, discovered leaves of the same species in a fresh-water deposit overlain by the curious gravel-bed containing Ancylus. In Jemtland, Mr. A. F. Carlson, in 1885 and 1886, discovered leaves of Dryas and Salix reticulata in calcareous tufa in several localities (4) far removed from the regions where these species now exist. In Norway nothing whatever was known of the ancient Arctic flora until last summer (1891), when, according to Prof. A. Blytt, leaves of Dryas octopetala were found in calcareous tufa at Leine (5). In Denmark the continued researches of Prof. Steenstrup have added many new localities (6) to the original ones mentioned above, not only in Seeland, but also from a private communication made to the author) on the isle of Möen (6'), in Northern Jutland (6"), and on Bornholm (6"). Turning to Switzerland, Prof. C. Schröter, of Zurich, has discovered three new localities for the glacial flora, and in 1880 I myself found leaves of Salix herbacea, Dryas octopetala, and Betula nana in a freshwater deposit near Hedingen (Canton Zürich), and leaves of the last-mentioned species underneath a peat-moss at Wauwyl (Canton Luzern), and in peat at Le Chaux de Fonds.

It ought also to be mentioned that Prof. M. Staub, of Buda-Pest, has lately described a fossil glacial flora from the Southern Carpathians, which, besides seeds of Pinus Pumilio and Pinus Cembra, also contains leaves of Dryas octopetala, Betula nana, and Salix myrtilloides, together with fruits of Tofieldia borealis, thus proving the existence of a somewhat colder climate than the present

one.

In 1880, I discovered a locality at Neetzka, in Mecklenburg, not far distant from Oertzenhof where I had found Betula nana in 1872. The new locality (14) yielded Dryas octopetala, Salix reticulata, Betula nana, B. odorata, and B. verrucosa, together with leaves of Myriophyllum, some other Salices and mosses, such as Hypnum scorpioides and H. fluitans. According to the manner in which the samples of clay were gathered, it is very possible that the species mentioned belong to different horizons.

Neetzka and Oertzenhof being the sole localities in

1 It is curious that Dryas octopetala has not yet been reported from the glacial plant-fossils of Great Britain, although it abounds in the glacial fresh water deposits of Sweden, Denmark, Germany, and Russia; and although the plant still lives in the mountains of Scotland, Yorkshire, and Wales. May not, however, the leaf from Crofthead which Mr. Mahony has identified with Scutellaria galericulata (Geol. Mag., vol. vi. p. 392) in reality have been a leaf of Dryas? The leaves of Scutellaria can hardly be preserved in the fossil state.

Northern Germany which until then had yielded fossil Arctic plants, while nothing whatever was known of the existence of Arctic plant-fossils in Russia, Prof. O. Drude, of Dresden, in 1889 expressed the opinion that the margin of the great northern inland ice might have been surrounded, not by an Arctic flora, but by a forest growth; and further, that such a growth may even have existed on the surface moraines of the inland ice itself.

I have lately tried to show, however, that this hypothesis is erroneous; but with the conviction that facts would prove the best arguments, I resolved to visit those portions of Western Russia and Northern Germany which I had not previously examined, and, thanks to the liberality of the Swedish Society for Geography and Anthropology, who gave me the balance of the Vega fund, I have been enabled to carry out my project, with the results communicated below. As my collections are, however, only partially worked out as yet, the present notice must be considered as only preliminary.

The circumstances under which the Arctic plantfossils occur are pretty uniform, and it may therefore be convenient to state them at once, instead of giving a description for every locality. In those parts of Western Russia and Northern Germany which I visited, the ground almost everywhere consists of a true moraine profonde (till) which has never been covered by the sea. Though marine glacial deposits are consequently absent in this area, fresh-water deposits, which have been formed in ancient lakes or ponds, are very abundant. These deposits consist generally in their lower part of a bluish clay or sandy clay, sometimes distinctly laminated, while the colour of the clay in the upper part is generally somewhat yellowish. This fresh-water clay is often covered by white shell marl, principally derived from the shells of fresh-water Mollusca; sometimes, however, by mud containing the remains of microscopical Algæ, fragments and excrements of insects and other minute fresh-water animals. Then comes the peat, terminating the deposit above-sometimes developed as a true peat-moss; at others, only as a peaty mould I to 2 feet thick. In places the peat is totally absent, ie. the fresh-water lake has been entirely filled up by the alluvial clay before the formation of peat had begun.

The Arctic plant-fossils are found principally in the clay, sometimes also in the white marl or mud, whilst only Betula nana ascends into the peat. Some freshwater Mollusca are found together with the Arctic plants -namely, some species of Pisidium, Limnæa ovata, Anodonta or Unio, sometimes also Cyclas cornea. By studying the distribution of the Mollusca in the different horizons, the order of immigration of the different species can be ascertained, and we know now very well the manner in which this has taken place in Southern Sweden. Besides Mollusca, the Arctic plants are often accompanied by remains of beetles and by Ostracoda, such as Cytheridea torosa and others; and in one locality in Scania I have also found abundant remains of Apus glacialis. Finally, it is in this horizon that the remains of the reindeer are principally found in Southern Sweden, Denmark, and Northern Germany.

When travelling in Esthonia and Livonia I had the advantage of being accompanied by the well-known geologist, Akademiker Fr. Schmidt, of St. Petersburg, and the success of our investigations was largely due to his advice. The Arctic plant-fossils were first discovered at Kunda in Esthonia (7), where the fresh-water marl and clay are used in the preparation of cement. The upper part of this deposit has yielded a great many bone implements of Neolithic age, which were described some years ago by the late Prof. Grewingk, of Dorpat, and antlers of reindeer are likewise present. The Arctic plants were obtained at a depth of 17 feet below the Petermann's Mitteilungen, 1889, pp. 282-290.

2 Engler's Botan. Jahrbücher, Bd. xui, 1891, Beiblatt Nr. 2).

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