masses we cannot doubt from their form were found interstratified with the other rocks of this neighbourhood, and from the trifling appearance of disintegration on many of them, we suspected them to have been quarried for the purpose to which they have been applied. We did not, however, succeed in finding the quarry, owing, perhaps, to the still very unfavourable state of the weather. We have since been informed by Mr. Jos. Woods, that he has seen the quarries in question in that neighbourhood, and that these masses are found as we had suspected. Rolled masses of this rock, both porphyritic and otherwise, prevail every where in the low ground and valleys, and have been much used as a building stone. On our return to Capel Curig, we passed the foot of Trefan, a mountain of considerable elevation, whose remarkably serrated outline, and rugged scarp attracted our attention, and induced the wish of ascending it for the purpose of becoming acquainted with the nature of its constituent rocks. But the extreme wetness of the weather deprived us of the power of seeing much that would have been highly interesting. Mr. Dawson afterwards presented us with a specimen of a rock having the appearance of a conglomerate, and resembling some already described as appearing near the base of Moel Shabod, and which he informed us prevailed on the ascent of Trefan. The same gen tleman showed us a small fragment of one of the two remarkable upright pillars on its summit, which resembled some of the small grained rocks, hereafter to be noticed, as occurring near the summit of Snowdon. (To be continued.) ARTICLE II. On Siliceous Petrifactions imbedded in Calcareous Rock. (To the Editor of the Annals of Philosophy.) DEAR SIR, Bath Easton, Oct. 2, 1822. THE perusal of the note occurring at p. xii. of the preface to the "Geology of England and Wales," has induced me to submit to a rude examination such specimens as I possess of siliceous petrifactions imbedded in calcareous rock. I wish that my results were more calculated to throw light upon their production, and that they may induce some one better qualified to pay the subject that attention which it demands. 1. Coral in separate Branches protruding from the Surface of Masses (apparently either Nodules or weathered Portions) of dark blue Limestone (Mendip Hills).-The exposed portion of coral entirely siliceous, and in parts studded with minute crystallizations of quartz. On exposing the mass to the action of diluted muriatic acid, I found that the siliceous matter of the coral penetrated but a very little way into the limestone; even at the point of entrance the branch became smaller, and its organic character much obliterated. 2. Siliceous Petrifactions of the Stems and Plates of the Encrinite beautifully preserved in Relief on the (weathered?) Surface of Limestone Blocks. (Barrington Cleve, and Mendips.)-On exposure to acid exhibited the same phænomena with the preceding. In both cases even the smallest nodules or plates of limestone exhibit in their interior, organic portions, of the same species with those silicified on their surfaces, but preserved as usual in calcareous matter. A lucky fracture, even while I am employed in transcribing my notes, has denuded for me a branch of coral, which is converted on the surface into silex, but almost from the point of entrance is continued in calcareous spar. The limestone in which these fossils are imbedded gave, upon solution in a dilute acid, a residuum of from six to seven per cent. consisting chiefly of silex in a state of minute division. It struck me forcibly that these and all specimens of the same nature, which I recollect to have seen from the mountain limestone, appear either to have been detached from the exterior of the strata, or to have occurred in small insulated masses. This, joined to the circumstance already noticed of the change which takes place in the substance of the fossil after its entrance into the limestone, induces a conjecture that the source of the silex is to be sought for in the iron shot marle which occasionally fills up the interstices between the calcareous strata. On the causes which may have operated to produce, either in this or any other formation of limestone, the alternation of marly or slaty beds, I do not venture to speculate. 3. Gryphites preserved in coarse Chalcedony, from Dunraven. -These are found both in the solid lias and in the marle which alternates with it. A portion of the former, in which a chalcedonic shell was totally enveloped, afforded with acid a residuum of silica mixed with a small proportion of alumina, iron, and bituminous matter. The whole residuum amounted to nearly 15 per cent. of which two-thirds at least must have been silica. In the lias which furnished these specimens, I observed large cornua ammonis having their interior partly studded with crystallized quartz. The composition of the lias beds, especially towards their exterior, is so variable that other specimens might possibly furnish a yet greater proportion of silex. 4. A Specimen of Chalcedonic Shell imbedded in a very Chalky Form of Green Sand (from near Stourhead, Wilts).-From the nature of the matrix, the action of diluted acid very readily extricated the shell (a portion of a large pecten.) The acid then attacked the shell itself, and before its action ceased, had dis solved a considerable portion of it, a fine siliceous powder falling during the process. The undestroyed portion of the shell remained as a thin irregularly shaped mass of chalcedony. On this of course acids had no further effect. The specimen, therefore, exhibits a singular instance of a shell preserved partly in siliceous and partly in calcareous matter. These are the only cases of this phenomenon which I have hitherto had the opportunity of examining. Believe me, my dear Sir, very truly yours, ARTICLE III. On the Geology of the Malvern Hills. (To the Editor of the Annals of Philosophy.) MY DEAR SIR, Bath Easton, Oct. 4, 1822. A SHORT residence at Malvern in the summer of 1821 enabled me to verify most of the statements contained in your brother's very accurate survey of its neighbourhood, and to observe some few circumstances, the detail of which (as they are unnoticed or not viewed in the same light, either by that gentleman, or by Mr. L. Horner), may; perhaps, be regarded as contributing somewhat more towards the history of that interesting tract. I would first notice the character of the two remarkable conglomerates connected with the syenitic rock. The first of these occurs in blocks (which I was unable to trace to their original site) a little southward of the road leading to the Wych. (The wall in particular which supports the ground in front of the cottage, named North Lodge, contained many specimens of it.) It is composed of amorphous nodules of the small-grained red syenite, abounding in felspar, imbedded in a paste, so precisely resembling the nodules themselves, as to preclude all supposition of its being a mechanical mixture. A recomposed granitic rock (as it has been termed) possessing nearly the same characters, was found by my friend Dr. Daubeny in loose blocks near Ardnamuchan, N. B. M. Bouè (Geologie de l'Ecosse, p. 22), mentions a rock of the same nature as occurring near the Fall of Fyers. (See also Dr. Macculloch's Classification, p. 580, G. 6.) Another conglomerate, evidently belonging to the same class, was found in situ on the road leading from Castle Morton Com * These are, if I'mistake not, the last rocks mentioned in Mr. W. Phillips's Catalogue. The former is probably that described by Mr. L. Horner, T. G. S. vol. i. p. 295. § 26. * mon to Ragstone Hill. In this both the nodules and the cementing mass are of a dark and apparently homogeneous trap, not much unlike that through which the passage of the Wych is cut. This rock, especially the imbedding paste, seems to decompose with great readiness into a greasy clay,t a character often observable in the less crystalline and obscurer forms of greenstone. The quarry from whence my specimens were obtained exhibited no traces of stratification. Both these conglomerates occasionally contained nodules of quartz. Whether they are to be considered as contemporaneous with, or posterior to, the formation of the great syenitic mass with which they are connected, I cannot pretend even to conjecture. Appearances certainly occur which might countenance the belief that there has been, to some extent at least, a second infiltration or injection of matter identical with one or other of the constituents of the original rock. Thus in one spot I found a vein of white felspar containing angular fragments of dark green trap. Some other of the felspar veins would, perhaps, be held to be true veins, and the dyke observed by Mr. W. Phillips seems to have every pretension to the character of a true dyke. At the north or rather north-west extremity of Ragstone Hill the greywacke appears in force, and assumes a much more characteristic aspect than in those points where it alternates with the transition lime. Its slaty variety here occurs as a very dark (nearly black) shale, the appearance of which joined with the resemblance which its compact form bears to some of the coal measures, has tempted some of the neighbouring cottagers to make trial for coal. This end of the Hill would, perhaps, be the best spot for studying the character of the greywacke, and its relation to the syenite. I have to regret that neither my time nor my health, would permit my accurately examining, or paying it a second visit. At the old shaft, known as Williams' Mine, I found no trace of metal, and was disposed to acquiesce in the general belief that the adventurers had been misled by the pseudo-metallic aspect of the Cat Dirt (disintegrating mica), until a lady who had examined the deads with greater care, informed me, and I afterwards observed myself, that some few portions of the rock contained very minute specks of yellow copper and patches consisting of, or at least coloured by, its carbonate. They were of very rare occurrence, and the whole quantity which I saw could not have exceeded a few grains. They who know the sanguine temper of miners will, however, understand that these must have * See Bouè, p. 130, for an analogous fact in dolerite (augite rock). On the Connexion of trap and syenite, see Dr. Macculloch on the Island of Rum. + Is it not this which has been termed by Mr. Horner and Mr. W. Phillips steatite? Hand specimens are met with in which it seems difficult to ascertain whether they belong to the trap or the greywacke formation. Is it possible that they may graduate into each other? Near been quite sufficient indications to ground a venture on. the debris of this mine the hornblende and epidote may be found crystallized mere distinctly, and the dark-green mica aggregated in larger and more characteristic masses than is usual. The latter (the mica) is of that variety which occasionally scratches glass. It fuses readily before the blowpipe into a greenish-black glass. The disintegrating variety (Cat Dirt) is more difficult of fusion, and the result more slaggy. I may add that the quarries of Ledbury have of late produced many specimens of a trilobite nearly resembling that of the South Welch transition rocks of Dynevawr and Built, and that calcareous spar of a very pure rose colour is found in large lamina interposed between the strata of limestone. I could not find it crystallized. If it occurs in that state, it must form specimens of singular beauty. Believe me, dear Sir, very truly yours, J.J. CONYBEARE. ARTICLE IV. Reply to Messrs. Young and Bird. By N. J. Winch, Esq. SIR, (To the Editor of the Annals of Philosophy.) Newcastle-upon-Tyne, Oct. 7, 1822. HOWEVER unwilling I may be to occupy your pages with controversy, yet as an honorary member of the Geological Society of London, I consider it a duty I owe to that body not to allow the misrepresentations of the Rev. Mr. Young and Mr. Bird, of Whitby, printed in your last number, to stand on record unanswered, particularly as the Society is mentioned in their letter. The hills and a portion of the flat country in the northeast of Yorkshire are now ascertained to belong to the lias formation; the upper beds consist of sandstone, shale, and limestone, with thin seams of coal, the lower bed of shale or alum slate, but the limestone and coal are not interstratified with the other beds throughout the whole district, and in many places the alum shale bassets out, or possesses a very thin covering, my critics' ideas of geology being formed only from the inspection of a very limited district." (See Introduction to Conybeare and Phillips's Outlines of Geology, p. xiv.) They have considered the upper strata and lower stratum as distinct formations, and upon this assumption the whole of their statements rest. On such false premises they attempt to convict me of what they term gross mistakes, but let my account of the outline of the lias be compared with Mr. Greenough's map, and the discre |