colour of ashes, and at this season (in the month of October), was not polished or smooth so as to be slippery; the hardness or consistence was such as to bear any weight, and it was not adhesive though it partially received the impression of the foot; it bore us without any tremulous motion whatever, and several head of cattle were browsing on it in perfect security. In the dry season, however, the surface is much more yielding, and must be in a state approaching to fluidity, as is shewn by pieces of recent wood and other substances being enveloped in it. Even large branches of trees which were a foot above the level, had in some way become enveloped in the bituminous matter. The insterstices or chasms are very numerous, ramifying and joining in every direction, and in the wet season being filled with water, present the only obstacle to walking over the surface; these cavities are generally deep in proportion to their width: some being only a few inches in depth, others several feet, and many almost unfathomable: the water in them is good and uncontaminated by the pitch; the people of the neighbourhood derive their supply from this source, and refresh themselves by bathing in it; fish are caught in it, and particularly a very good species of muliet. How these crevices originate it may not be easy to explain. The lake contains many islets covered with long grass and shrubs, which are the haunts of birds of the most exquisite plumage, as the pools are of the snipe and plover. Alligators are also said to abound here.' pp. 64, 65.

It appears at times to be of a very yielding nature, and is said to have swallowed up, in the course of a night, the cauldrons which the Spaniards had erected upon it with a view to convert the bitumen to economical purposes. The negro

houses of the vicinity are also frequently twisted by its subsiding. As the substance is in every respect well adapted to supply the place of pitch, the importance of so vast a reservoir, when justly appreciated, must be very great.

The Souffriere, of the Island of Montserrat, is briefly described by the same author, in the seventh paper. It is re markable that almost every island in the Western Archipelago, has a spot thus denominated from its volcanic phenomena. Dr. Nugent mentions Nevis, St. Kitts, Guadaloupe, Dominica, Martinico, St. Lucia, and St. Vincent. The last has unfortunatly of late been an object not merely of curiosity, but of terror. The souffrieres of Guadaloupe and St. Lucia, are also decided volcanos. Our author thinks these circumstances sufficient to refute the idea of most who have touched upon the formation of the West Indian Islands, that they originally formed parts of the American continent, and that the encroachments of the sea have left only the higher parts of the land as insular points above its present level.' Some, he admits, from the primitive rocks which they contain, may be ascribed to this origin: but it does not, he thinks, apply to such as are formed of organic substances, or by a volcanic agency. We must, however, observe, that alluvial tracts are

generally formed around or upon a portion of older strata, as Dr. Nugent has himself shewn in the instance of Trinidad; and that volcanos as frequently perforate, or rest upon primitive rocks, as arise from the bottom of the sea. Alluvial or volcanic strata may at present compose the whole of the visible surface of many of these islands; but this by no means demonstrates, that their original basis is not part of the ancient continent. Indeed it requires the admission of a very considerable latitude in the meaning of the term volcanic, to make it include the soufirieres of most of the islands: and though every extensive evolution of heat will be called a volcano, by such as classify the appearances of nature according to their effects, it is evident that the geologist cannot apply the term, vague as it is, to a mass of pyrites, or a stratum of coal in a state of ignition. The justice of these observations will sufficiently appear from the author's description of the spot.

the

• We continued our ride, till we came to the side of a very deep ravine, which extends in a winding direction the whole way from one of the higher mountains to the sea. A rugged horse path was traced along the brink of the ravine, which we followed amidst the most beautiful and romantic scenery. At the head of this ravine, is a small amphitheatre formed by lofty surrounding mountains, and here is situated what is termed "the Sulphur." Though the scene was grand and well worthy of observation, yet, I confess, I could not help feeling a good deal disappointed, as there was nothing like a crater to be seen, or any thing else that could lead me to suppose the place had any connection with a volcano. On the the north, east, and west sides, were lofty mountains, wooded to the tops, composed apparently of the same kind of porphyry we had noticed all along On the south, the same kind of rock of no great height, quite way: bare of vegetation, and in a very peculiar state of decomposition: And on the south-eastern side, our path and the outlet into the ravine. The whole area thus included, might be three or four hundred yards in length and half that distance in breadth. The surface of the ground not occu pied by the ravine, was broken and strewed with fragments and masses of the porphyritic rock, for the most part so exceedingly decomposed, as to be friable and to crumble on the smallest pressure. For some time, I thought this substance, which is perfectly white and in some instances exhibits an arrangement like crystals, was a peculiar mineral, but afterwards became convinced, that it was merely the porphyritic rock singularly altered, by a strong sulphureous or sulphuric acid vapour....Amidst the loose stones and fragments of decomposed rock are many fissures and crevices, whence very strong sulphureous exhalations arise, which are diffused to a considerable distance; these exhalations are so powerful as to inpede respiration, and near any of the fissures are quite intolerable and suffocating. The buttons of my coat, and some silver and keys in my pocket were instantaneously discoloured. An intense degree of heat is evolved, which added to the apprehension of the ground crumbling and giving way, renders it difficult and painful to walk near any of these fis VOL. VIII. 51

sures.

The water of a rivulet which flows down the sides of the moun. tain and passes over this place is made to boil with violence, and becomes loaded with sulphureous impregnations. Other branches of the same rivulet which do not pass immediately near these fissures, remain cool and limpid, and thus you may with one hand touch one rill which is at the boiling point, and with the other hand touch another rill which is of the usual temperature of water of that climate....On the margins of these fissures, and indeed almost over the whole place, are to be seen most beautiful crystallizations of sulphur."* pp. 186-188.

The sixth paper, by Dr. Berger of Geneva, on the physical structure of Devonshire and Cornwall, is the longest in the volume, and unquestionably one of the most attractive. We regret that we are obliged to confine our account of it within limits so inadequate to convey even the more important of his observations on this interesting portion of our island. After some remarks on the chalk strata, and the formation of the flints which they contain, a formation which extends a hundred and fifty miles from east to west along the southern coast of Britain, Dr. Berger examines the transition country around Exeter, consisting of sand, gravel, sandstone, and amygdaloid in various degrees of cohesion. The strata at Heavitree, near Exeter, dip S. E. at an angle of about 15°. To this, in the south, succeed limestone strata which do not appear to be perfectly discriminated, though at Flying Bridge our author found, what is termed by the Wernerians' the transition limestone' in its true character. A few miles east of Oakhampton, the grauwacke formation commences, which attends both sides of the whole of the low mountain chain of Devon and Cornwall, the central part consisting of granite, and the south-western terminating in a serpentine formation. Brown Willy, near Bodmin, is the most elevated point, being 1368 feet above the level of the sea. Dr. Berger observes, that this range presents a regularity in its composition, rarely found in great chains.' The Alps have calcareous moun tains on the north, while to the south the schistose strata extend to the plains; and similar differences between the opposite sides occur in the Pyrenean and Siberian chasms of mountains. The grauwacke is either compact or slaty; the latter variety is called killas by the miners, and is very frequently metalliferous. Our author mentions that he has never found in it any impression of crganic bodies, nor is he aware that it has ever been found to contain them;' but we think he is mistaken, as it certainly does contain vegetable impressions in the Karz, as noticed by Blumenbach; (Handb. der natur geschichte) and we are much deceived if we have not found casts of fusiform madrepores, and of a striated bivalve, in our British

*The reader may compare this description with that extracted from Mr. Hooker's publication on Iceland, in the Ecl. Rev. for June 1812.

strata. The serpentine commences at Port-hallo accompanied by metalloidal diallage, and forms the Lizard point. From Mullyan to the N. W. the grauwacke continues, and forms the highest cliffs of this part of the coast. Dr. Berger mentions á curious fact at the mouth of the river Loe:

The river forms a kind of reservoir at a little distance from the sea, which I found to be one hundred and sixty paces at low water, from which the water runs into the sea by a subterranean passage, The water in the pool is fresh, though the bar of sand between it and the sea is not more than twenty feet high. This shews that the tides do not rise very high, and the inhabitants assured me that at no time of the year did they find the water at Loe Pool become salt. I tasted it repeatedly, and found it quite fresh. pp. 140, 141.

An idea is entertained, and discussed much at large by Dr. Maton, that the sea has encroached very considerably upon the land in the neighbourhood of Mount's Bay, and even the number of churches swallowed up has been stated; but Dr. Berger is of opinion, that if such a catastrophe ever took place, it must have been previous to the deposition of the grauwacke formation, consequently at a period extremely remote from that of any historical record whatever. At the extreme point of Cornwall, the descending granite at last excludes the grauwacke, which is only seen at low water on the shore at Mouse-hole. Here Dr. Berger notices the veins of granite which intersect the grauwacke, a phenomenon to which so much importance is attached by the Huttonians, and which has also been observed in many other places. We cannot here enter into the dispute between the favourers of the two systems, but think Dr. Berger perfectly correct in stating that they by no means prove, that both the granite and the veins are of later formation than the strata of grauwacke.' The Logan rocks, or rocking stones, our author ascribes to the mode in which granité disintegrates, but he does not admit that granite is ever stratified. Returning along the northern side of the chain, the blocks of schorl rock, which probably form a subordinate bed in the granite, attract attention. The strata of grauwacke which, on the southern side of the chain slope to the south, were here found, as might be suspected, to incline towards N. W. that is, in both instances, from the granite. Dr. Berger remarks that the productive veins range in a direction from E, S. E. to W. N. W., those of copper being generally longer than those containing tin; the latter are found exclusively in the granite, but the former though chiefly in the grauwacke, are not confined to that stratum. The cross courses, or unproductive veins, intersect the metalliferous veins nearly at right angles, and are evidently of later formation. The regular mines worked

in Cornwall in 1800, amounted to 99; of which 45 were of copper, 28 of tin, 18 of copper and tin, 2 of lead; the rest produced silver, cobalt, and antimony; and at present some mines of manganese are opened. To this paper and to another, by the same author, on the geology of some parts of Hampshire and Dorsetshire, tables of the heights of places above the level of the sea, by barometrical admeasurements, are aunexed.

The eighth paper, on the Wrekin and the great Coalfield of Shropshire, by Arthur Aikin, Esq. displays great ability, and is of considerable importance, by adding to our knowledge of the extent and situation of those deposits of fuel, on which the commercial advantages of this kingdom so much depend. The great Shropshire coal-formation lies adjacent to the old and red sandstone, which occupies so large a portion of the north western part of England, and to which the rock-salt district is subordinate. At the Madely Colliery, a pit has been sunk through all the beds to the depth of 729 feet: they are there no less than 86 in number, but vary, as in most other coal fields: for it is certain, notwithstanding the frequent representations to the contrary, that beds of coal and the intervening strata, are liable to very considerable alterations in thickness, though their increase or decrease is generally so gradual, as not to be perceptible in the works of each separate mine. Mr. Aikin is mistaken in referring the peculiar configuration of the curl-stone to an animal origin; it occurs in the common argillaceous ironstone after torrefaction, and is well described by Mr. Martin in his Petrificata Derbiensia. (Plate 27.fig. 4.) The coal formation rests upon a limestone, which appears to be identified with that of Dudley by the occurrence of the entomolithus paradoxus. The great mass of the Wrekin, the Lawley, Caer Caradoc, &c. consist of an unstratified trapformation,' comprising felspar, and green-stone rocks, the latter of which affect the magnetic needle.

‹ These rocks are incumbent on highly elevated strata of transition slate on the eastern side of this mass it appears, That there is a great deposit of stratified rocks, consisting of quarry grit; of a micaceous sandstone, nearly allied to greenstone; of a sandy slate-clay; of limestone, laty marle, and sandstone slate, in alternating beds; and of the independent coal-formation; all rising up parallel, or nearly so, with the trap at a horizontal angle, the magnitude of which decreases, in proportion to the distance of each bed from the trap... That on the western side the mass of deposits is very small, consisting of a sandstone composed of angular fragments, on which rests a thin, broken coal formation: That the old red sandstone bounds the whole of this series of rocks on the east, north, and north-west, but though in contact, appears to be perfectly unconnected with them.' P. 212.

The amygdaloid containing in its vesicles concretions of