er part of the Cordeliera of the Andes, especially in the southern hemisphere. To generalize more rapidly and more extensively than actual observation authorises us to do, is as much to be guarded against as any error in philosophy, and has produced effects as hurtful to the progress of truth. Dr Berger indeed has this apology, that he has studied in the school of Werner; and we know of none where the worship of this particular idol is more strictly enjoined.

Dr Berger is the first mineralogist that has given a general name to the rocks that lye on the granite ridge of Cornwall, and has pronounced them to be Grauwacke; a rock, he says, composed of separate silicious particles, united by an argillaceous cement with a little magnesia and iron. We believe that it is true, that the Cornish rock here meant is to be referred to the tribe of the Grauwacke; at the same time we must object to the definition above, if it is to be understood as general. The particles united by the argillaceous cement of grauwacke consist often of felspar, and have the appearance of proceeding from the disintegration of porphyry. The term applied by the Cornish ⚫ miners to this rock is Killas; which, on account of its better sound, we should very much wish to see substituted for the uncouth German name of Grauwacke.

Dr Berger began his survey by the valley of the Erme, which opens at Ivy Bridge. By this valley he ascended to the elevated plain of Dartmoor Forest, which occupies a considerable extent of Devonshire, and sends a number of streams to the opposite sides of the peninsula, that is, into the English, and the Bristol Channel. From thence he seems to have gone by Launceston and Bodmin to Truro, visiting Grampound, however, and the adjacent coast. From thence he examined the country about Falmouth, the Lizard, Mount's Bay, the Land's End, returning by St Ives, Redruth, and the coast of the Bristol Channel. The objects of chief curiosity in these parts he seems to have examined; and we only wonder to find him make no mention of the Roach Rocks, which are certainly very remarkable. *

Dr Berger takes notice of the decomposed granite in the state of Kaoline, which affords the porcelain earth so much prized for

*These rocks are situated between Bodmin and Truro, and form a singular pile of natural ruins, that has been mistaken for a druidical monument. They cover nearly an acre of ground, and rise in steep precipices on every side, to the height of about 60 feet. They are composed entirely of quartz and hornblende, very much crystallized, and the former in much the largest proportion. The size and irregularity

for the manufacture of china, and which is indeed one of the characteristic features of Cornwall. The plain in which this earth is found is some miles in extent, and belongs to the southern boundary of the granitic chain. One of the most elevated points of it, and which is in the neighbourhood of the principal quarry of the porcelain earth (china pit), is 830 feet above the level of the sea. This granite, the felspar of which forms two thirds of the mass, appeared to be less decomposed hear the borders of the plain, than in the central part. In this last place, it has rather the appearance of a porphyry with a pulverulent base, of a whitish colour, in which crystals of quartz, and some plates of mica, are loosely included. It is used in this rough state in the manufacture of porcelain, in the same manner as the Chinese make use of petuntze, by mixing it in certain proportions with the porcelain earth that is obtained by washing and frequent precipitations. Crystals of a compact and earthy felspar are occasionally met with in this decomposed granite, of a much larger size than usual.

One of the rocks which Dr Berger has particularly described, is the serpentine of the Lizard Point and its vicinity.

This rock is not homogeneous in its composition. The colour of the base is usually leaf green; it is often conchoidal, breaking into large broad flakes with sharp edges. It is also frequently striped with red, which appears to be owing to the oxide of iron. Small threads of tender yellow steatite are seen running through it, and it is often traversed by veins of whitish asbestos. Sometimes this serpentine passes into a hard steatite, disposed in curved lamine, and having a fibrous fracture. This serpentine, though surrounded on all sides by rocks of Killas, does not appear in immediate contact with it. At the northern boundary of the serpentine, (where Dr Berger entered it), a rock intervenes, composed of felspar and diallage, or granular actynolite. On the S. S. W. of the village of the Lizard, there are some beds of mica slate, which appear subordinate to the serpentine.

Though the Doctor has treated, at some length, of the dif ferent formations of serpentine, and of the rocks that accompany them, he makes no mention of a circumstance that might be expected to arrest the attention of a Wernerian geologist. In the arrangement of rocks adopted in that school, if we mistake not, two formations of serpentine are admitted; one the 9th, the other the 15th of the primitive formations, counting from

irregularity of the fragments, and the ruinous appearance of the whole, mark the destructive operations of time in stronger characters than it is usual to meet with in a country so little mountainous as Cornwall.

from the granite upwards; and neither of them belonging to the transition or intermediate rocks. In Cornwall, however, the serpentine is contained between transition rocks, which appear on both sides of it. What it rests on below, is unknown. It may lye immediately on the granite; but this much is certain, that all round it is the killas. Here, therefore, is a great anomaly in the arrangement of rocks, if there be any truth in the Wernerian system. The fact, however anomalous in respect of artificial arrangement, is not singular in nature; the coast of Ayrshire in Scotland, between Giryan and Ballintrae, affording an example of the same kind.

The next object of importance is St Michael's Mount, which, from the singularity of its figure and situation, is not less interesting to common observers than it is to mineralogists, from its composition and structure. The south side of the mount, on which the castle is situated, is nearly precipitous, and is composed, from top to bottom, of a granite split into irregular masses. At the base, and on the sides of this granite rock, lyes the killas; and a circumstance that has attracted great notice, is the number of granite veins which penetrate into the superincumbent rock, especially towards the south, where the steepness is greatest. These veins have so much the appearance of shooting from the granite into the killas, that they have appeared, to many mineralogists, a proof that the lower rock is of later formation than that which lyes above it. To this position, however, Dr Berger is unwilling to agree. I conceive,' says he, that at the time the grauwacke was deposited upon the granite, the water in which its particles were suspended, meeting with portions of the granite, a little more elevated than the plane of the surface, left them exposed, and filled up the spaces between." What have been called Granite veins, are therefore, on this supposition, no more than inequalities in the rugged surface of the granite, surrounded at their sides by the killas, and left bare in the more prominent parts. Dr B. must be aware, that this hypothesis admits of being confronted with the facts. If, on cutting into the rock, it is found that these apparent granitic veins do not merely proceed from the granite at one end, but are united with it for their whole extent, and only form a sort of edge rising above the rest of its surface, his opinion will have great plausibility But, if the contrary is the case, if the supposed veins are sur rouuded by the killas, above and below, and are joined to the granite only at one end where they are thickest-in a wond, if they are like the roots of a tree penetrating into the earth, his supposition falls entirely to the ground. The trials neces

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sary for determining this question have not, that we know of, been made at St Michael's Mount: but they have been made in other places; and the fact has been found to be as last represented. This is true of the granite veins near New Galloway, of which, as Dr Berger remarks, Sir James Hall caused a model to be constructed.

• How comes it,' says Dr B., if the origin of these veins is to be ascribed to the action of a force from below, that they ⚫ occur in so few places? and how comes it that the grauwacke, as it approaches the junction between it and the primitive rock, continues diminishing in thickness?'

To these two questions, we believe, it would be easy for a Huttonian geologist to reply ;-in the mean time, we must observe, that the Doctor passes, in profound silence, over the obvious objections to his own hypothesis. In particular, he does not attempt to explain how such a number of thin plates of granite, as the veins at St Michael's Mount are supposed to consist of, were formed on the surface of a rock without any mould in which they could be cast, and how they remained projecting from that surface, without any support, from the time of the formation of the granite to that of the transition rocks.

f Dr B. is of opinion, that the granite of Cornwall is not stratified; and he thinks, that true granite is never found possessing that character. The opinion," says he, that granite is stratified, is one which I cannot adopt, even after having visited those places where Saussure thought he had discovered the strongest proofs in favour of it.'

In this opinion we are very much disposed to acquiesce; and we think it is valuable, in such a case, to have the judgment of one who has examined granitic rocks in such various situations, and particularly those in which their disposition into strata was thought to be most clearly ascertained.

The observations, made in the course of this survey, on the inclination and bearing of the strata, are less numerous and pre'cise than might have been expected. The killas is, in generel, represented as lying conformably on the granite on both sides of the main ridge. This, however, we believe, is not universal;--and, if we are not misinformed, is sometimes in vertical beds transverse to the ridge just mentioned. In one instance, Dr B. takes notice of a fact that is very much of this kind; that though, on the south slope of the mountain chain of Cornwall, the strata of killas dip S. S. E., near Mount's Bay they dip N. N. W.-that is to say, they dip towards the granite, and instead of being laid upon its slope, or placed conformably, as it is called, are abutted against it.

In speaking of the mines, the Doctor observes, that Werner has brought forward so many facts, in support of the two fundamental positions, that veins have been originally open fissures, and that they have been filled from above, that this theory scarcely receives a greater degree of stability by any of the further proofs which are daily discovered. We readily admit, that the first of these positions is very well established ;—the proofs of the other seem to us extremely inconclusive-founded, as they are, upon that string of unsupported postulata which was taken notice of in a former Number of our Journal, and which we believe to be nearly unexampled in any work that presumes to consider itself in the light of a theory founded on experience and observation.-The question concerning the minerals that have come from above, and those that have come from below, is not to be so easily resolved:-it must require a patient and candid examination; and, above all things, a determination to resist eveevidence not founded on the most strict analogy, or the most rigorous induction. The fact which the Doctor adduces of pebbles, found in a mineral vein 250 feet below the surface, is certainly in point; but, in strictness, it only proves, that veins were open fissures, (which nobody presumes to deny); and that some of the materials that fill them may occasionally have fallen in from the top.

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On the direction of the veins in Cornwall, he remarks that the productive veins extend from E. S. E. to W. N. W. Some of the veins penetrate to a great depth,-such as 140 and 180 fathoms; and in passing from one species of rock to another, they generally change their degree of richness. There are other veins which intersect the former nearly at right angles, and are called cross-courses. Some of the most considerable of these extend from sea to sea; and, as the Doctor says, consist of marl or clay. But, if we mistake not, there are among these cross veins, some that contain copper, and that are in all respects mineral veins. The veins of granite and porphyry are also in the number of the cross-courses. They are evidently of posterior formation to the former, which they generally disturb and turn out of their course at the points of intersection.

The mines of Cornwall are very numerous; and it appears, that, in the year 1800, the number wrought was not less than 99. Of these, 45 were copper-28 tin-18 copper and tin-2 lead1 lead and silver-1 copper and silver-1 silver-1 copper and cobalt-1 tin and cobalt-and 1 antimony. To these may be added some mines of manganese, which were not worked when this enumeration was made. (p. 167.)