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METEOROLOGICAL JOURNAL FOR DECEMBER, 1835; KEPT AT BLACKHEATH ROAD. Barometer. Thermometer.
Clouds. Wind. Wind.
Solar Daily Rad. 9 A.M. 3 P.M.' Min.
7 2 S.
Temperate; evening and night cloudy and squally.
Fine clear atmosphere.
2 S. S.W.S.
Cloudy A. M.; much loose scud.
S.W. W.SW. Tem. A. M. ; a shower at 3 P. M.; air cooler; clear night.
W.S. W. S.W.
Cirro-cum, into cirro-stratus; much precipitation,
Temperate; cirro-stratus; resolving into a fog.
Cloudy throughout; air calm and close.
S.W. W.N. W. Overcast; rain at night.
Windy; flying clouds and cold; clear at night.
Small rain A.m.; clear frosty night.
Frost severe; air clear.
( Cloudy and lowering; cirro-cum, and cirro-stratus. Sun. 13 30.450 30•450 28.9 38.4 9.5 33.7 28 1 1101
Clear; night cloudy and misty.
S.E. Close, with drops of rain; damp and foggy.
Ditto, misty (stratus); cloudy; air getting damp.
Snow fell in the night; strong wind with small granular
Frost, with thick ice; cloudy with scud.
Ditto, ditto; overcast and dark with stratus and fog.
Ditto, ditto; dismally dark and misty.
10 0 0 W.
Ditto; much rime; sun just visible through a dense red
Ditto; clear at noon; cloudiness came on in the evening.
Cloudy; a thaw; cirro-cumulus.
Overcast and mild.
N.W. N.N.E. Ditto; a squall from n. about 3 P. M.; air getting cold.
Hoar-frost; cirro-cum.; P.M. dense fog and frost.
| Mean at 3 4. M. 30:366
Max. of Temp. 51.4 the 1st. Min. of
Mean Temperature 35.13 11
Solar Variation 7°82. do. 29.440 the lst.
Min. of do. 18.7 the 26th, Min. of the Rad. 15° the 27th. Rain fallen 0.49 inches.
MAGAZINE OF POPULAR SCIENCE,
JOURNAL OF THE USEFUL ARTS.
RECENT RESEARCHES IN GEOLOGY. GEOLOGY is a subject of immense extent; and the discoveries which are made in it almost necessarily proceed by slow steps and minute details. Hence it would be utterly impossible, even in a memoir of considerable length, to give a complete and comprehensive survey of the recent progress of this rapidly advancing Science. But here, as in all sound inductive researches, the accumulation of particular facts generally terminates, after a while, in the developement of some great general principles. When such epochs occur, it is often very practicable to condense into a short compass, and in a generally intelligible form, a statement of the results so obtained. This is what we shall attempt, in the following article, with respect to one or two leading subjects of geological inquiry, which have not only excited peculiar interest of late, but also have important bearings on the principles of the Science, and on some of the most instructive inferences and contemplations into which we are led by the study of it.
The conclusions of geology, like those of every other part of inductive science, must be grounded on the sole authority of well-ascertained and classified facts; and we must be guided to them, neither by random conjectures, nor the dictation of authoritative opinion, but by the sole pursuit of well-founded natural analogies. We must seek to interpret the past from the present, and advance from the known to the unknown.
Proceeding on such principles, then, we shall presume that our readers will acknowledge the force of the reasoning by which it is inferred that where two beds, or strata, lie one over the other, the former was deposited or formed subsequently to the latter ; that each one of the vast number of lesser beds or layers, of which even a small thickness of any stratum is composed, were all formed one after another; and, when we come to distinguish the larger divisions and classes of strata, by the fossil remains of plants and animals, which we find embedded, and often completely mineralized in them,—that these are the remains of creatures which actually lived and died during the period at which the depositions took place respectively; and that the lowest rational estimate we can form will not allow us to suppose any short or limited period of time as requisite for the formation of any one bed, the enclosing in it of all its organic remains, and (marine or aquatic as those remains so universally are) its elevation from the bottom of the primæval ocean into dry land.
Pursuing our researches on these simple and truly philosophic principles, we are brought in succession to recognise an immense series of deposits, characterized by organic remains, in which the skill of the naturalist and the anatomist detects species, genera, entire orders of living VOL. I.
beings which do not now exist. The deposits in which these occur, now in a great degree hardened and consolidated into rocks, are thus characterized as distinct formations, which have gradually emerged at successive remote epochs, at incalculably long intervals of time. Other classes of phenomena are observable in a series of rocks of a different texture, and wholly destitute of organic remains, which appear protruded, as it were, among and through the others : having, in many cases, an exact resemblance to the effects of existing volcanoes,-and in all, following a close analogy to such modes of erruptive action.
We shall in the following sketch presume no further on our reader's acquaintance with the subject than to the extent here briefly described. The names given to the successive leading groups of formations, which all over the world succeed one another in this order, are principally, the tertiary (or newest), above the chalk. The secondary, from the chalk inclusive to the coal formations : then those which have been called transition; and, lastly, the primary, of crystalline texture, without organic remains, and bearing marks of being upheaved, protruded, or forced through all the others, in the way that masses of melted matter are now forced up by volcanic action.
Silurian and Cambrian Formations. Mr. Murchison and Professor Sedgwick have been for a long time directing their joint labours to the elucidation of the rocks usually confounded together under the unmeaning name of “ Transition,” comprising all the series intervening between the old red sandstone and the primitive rocks. They have been minutely examined by these two eminent geologists, as developed in Wales and the part of England adjoining, and they have succeeded in dispelling almost entirely the obscurity in which the nature of these rocks has been long involved.
From beneath the old red sandstone, there rises out this considerable group of rocks which, taking them in the order from upper to lower, Mr. Murchison has named the Ludlow, Wenlock, Caradoc, and Llandeillo formations, each being distinguished by characteristic organic remains, and frequently by subordinate beds of limestone. These beds form a well-marked connected group, interposed between the old red sandstone and the slaty-grauwacke of Wales. Hence it seemed very desirable to apply some distinctive name. So great have been the recent advances in geology, that the term “transition,” formerly applied, has (as we observed above) now become wholly unmeaning, and, in fact, conveys incorrect impressions. Hence these geologists have adopted the name “Silurian System,” (from the Roman name for this part of Wales ;) and this they subdivide into the “ Upper Silurian," comprising the two first of the four classes named above,—and the “ Lower,” including the two last.
Beneath these appear the various slaty rocks, which are common to Wales and Cumberland. These Professor Sedgwick has minutely investigated ; and divides them, according to order of superposition, into upper, middle, and lower. The upper formation is seen in the chain of the Berwyn mountains, and is thence expanded over a large part of South Wales, including Plinlimmon, it contains in general less calcareous matter, and fewer organic remains, than the Silurian systems. The
middle Cambrian includes the Merionethshire ranges and Snowdon, containing a few organic remains, and some highly calcareous slates, but no beds of limestone. The same group is largely developed in Cumberland. The lower or oldest Cambrian group occupies the south-west of Caernarvonshire, and much of Anglesea. It contains no organic remains.
In this rapid sketch, we, of course, can do little more than explain the nominal distinctions which have been thus laid down. But it inust be understood, that they are far from being mere distinctions of names. They involve essential characteristics of extensive geological districts, and serve to bring under a luminous classification a series, of great importance to a connected knowledge of British strata, which has long been involved in obscurity from want of such a principle of arrangement.
A full account of these researches was given at the Dublin meeting of the British Association; and elicited, besides the encomiums so justly due to the talents and perseverance of its authors, many able illustrations and remarks; especially from Mr. Greenough, who considered that similar principles of classification might very probably be extended to other regions; and from Professor Phillips, who made some highly interesting observations on the distribution of characteristic organic remains in rocks, especially those here considered. He dwelt upon the important fact, so utterly destructive of the favourite hypothesis of some geologists and cosmogonists, of a gradual advance from the simplest to the most complex forms of animal life, as we advance to the newer rocks ; that in these Silurian groups, though we find a diminution in the number of fossil species in the older rocks, yet they exhibit no inferiority of structure or organization. They belong to extinct classes. Among beings of lower organization, as among shell-fish, some single species may be found even in rocks so ancient as the Silurian system, which also now exist; and he was hence led to remark, that it is not by any single genus, but by a combination of co-existing genera that strata must be identified.
Fossil Fishes. The natural history of fishes has been generally considered more obscure than that of any other of the great divisions of the animal kingdom; and it has been almost entirely through the labours of M. Agassiz that a new light has been thrown over it, by tracing out, as he has done, a new principle of classification : by this the whole science has been remodelled. It is also a singular circumstance in this investigation, that (contrary to the usual order of procedure) the study of the fossil remains of fishes has been a material source of elucidation for understanding the relations and classification of existing species.
The great principle of classification adopted by M. Agassiz, is derived from the nature of the external covering, or scales. The peculiar form and structure of the scales differs essentially in different classes of fishes; and the nature of the covering, which protects the animal externally, is found to bear a direct relation to the internal organization. Here then there appears a principle of relation which, doubtless, depends upon some essential modification of the animal character, and thus may fairly afford a satisfactory ground of a real distinction and classification of species. This principle, then, M. Agassiz has adopted; and, in following it out, has arrived at a grand distinction of fishes, under four principal orders, characterized by the peculiar nature of their scales. They are termed, 1. Placoïdians, 2. Ganoïdians, 3. Ctenoïdians, and 4. Cycloïdians*.
Of the whole number of species now known to exist, more than three-fourths belong to the two orders of Cycloïdians and Ctenoïdians, the other fourth to the remaining two. Whereas, of the species whose fossil remains we find imbedded and mineralized, none of the two orders last-named have been found in any formations below the chalk; whilst in the lower or older formations we have abundance of the other two kinds. The proportions of these in the different formations are very remarkable, and have been carefully traced by the persevering industry and skill of M. Agassiz.
In the most recent or tertiary deposits, not only the fossil orders and
genera, but also the species, approach nearly in character to those now existing : though he has not found more than one species exactly the same.
Those of the formation called “crag,” in Norfolk, are allied to the species now inhabiting the tropical seas. In the London clay, the beds in the basin of Paris, and at Monte Bolca, about two-thirds belong to existing genera.
In the formation next below these, the chalk, about one-third only belong to existing genera.
In the formations older than the chalk, there is not a single genus identical with the recent. The oolitic series, to the lias inclusive, forms by its species of fossil fish a very natural and well-defined group. The weald formation is included in this, in which M. Agassiz did not find a single species referrible even to the genera of the chalk.
Throughout the series of rocks deposited in these epochs, the two orders which prevail by so large a majority (as above stated) in the existing creation, are not to be found. New species have since been created; the whole genera formed of all those species are new, not merely in a few instances, but through such a range and extent, that even the entire order comprising those genera is new. In these older strata, on the other hand, different species, genera, and orders, existed in proportional abundance, most of which have since died away and disappeared ; and the two great orders which at the present day form a small minority, were then predominant.
The most striking characteristics, perhaps, of these periods are the predominance of those Ganoïdians which have a symmetrical caudal-fin; and those Placoïdians, which have their teeth furrowed on both sides, and have large thorny rays on the dorsal-fin. These fossil rays had long been known, but their real nature was wholly misunderstood.
In the formations below the lias, the character, above stated, in the tail-fin of the Ganoïdians is entirely changed. Instead of a tail parting
* These names are derived from Greek words, describing the shape and appearance of the scales. 1. From that, a table or broad surface, the scales being large.
auty or splendour; from the bright enamel with which they are armed.
3. From zrels, a comb, the scales being formed with teeth. 4. From xvidos, a circle, the scales being round.
2. From gavos,