The consideration of the subject of Denudation requires so extensive an acquaintance with Forms of the Ground in a field large enough to embrace all countries, that general conclusions must be advanced with more or less reserve, in proportion to the extent of our research.

Since the occurrence of Chitons, in the Mountain Limestone of Settle, was noticed by one of us, in 1862, other remains have been found in the same rock, as well as in the Carboniferous Limestone and shales of Scotland. The former were discovered, as before, by Mr. J. H. Burrow, of Settle, who has kindly placed them in our hands for description.

At the meeting of the British Association held in Birmingham in 1865, Dr. Voelker directed attention to the discovery of a bed of Phosphate of Lime in North Wales, and entered into particulars concerning its chemical composition, and economical value. same thickness and relationship to the adjoining beds. We thus infer that it was deposited in a somewhat shallow sea, not much varying in depth, or subjected to disturbing influences. The strata in which it occurs are rightly marked upon the government maps as “reversed,” dipping, as they do, away from instead of towards the adjacent Llandovery and Wenlock beds.

I owe my acquaintance with this interesting fossil to Mr. S. Stutterd, who kindly forwarded it to me for my inspection. It is from the Stonesfield Slate, and is preserved in limestone, but is only a cast formed in the matrix left in the rock after the organism itself had disappeared. The core had been hollow, or composed of a more speedily perishable material than the parietes, and so it rapidily disappered, permitting the empty axis to be filled with fragments of shells and calcareous sand. Externally, the cylindrical fossil is formed of sub-quadrangular peltate plates, with irregular undulate dentate margins, the projections of each of which fit into the undulations of the surrounding plates, and are arranged in linear series. A transverse section (Plate VIII. Fig. 2b.) shows each of these external plates to be the closed termination of a short tube, that has in the transverse section a hexagonal form. These tubes are filled in with a darker material, which, unfortunately, is without structure, and any determination of the affinities of the fossil must depend entirely on the external form, and the arrangement of the parts. Of necessity, these are defective and unsatisfactory materials; nevertheless, the fossil seems to me to present so remarkable an appearance, and so close an approximation to a portion of the inflorescence of an Aroideous plant, that I do not hesitate to refer it to this family; and I entertain the hope that one result of this notice and the accompanying figure may be to draw some attention to the fossil, which seems to be by no means rare, and so supply the means for more completely establishing its affinities.

I came accidently upon the deposits which are the subject of this brief notice, the afternoon before I Left Llandudno last April. Want of time prevented my making more than a hasty examination of them, but I think that they will repay any one who happens to be visiting Llandudno this summer, and will devote a day or two to them.

The strata lying above and below the Lingula Flags have already been well described and illustrated: the Menevian Gronp below, by Messrs. Salter and Hicks, and the Tremadoc Group above, by Messrs. Homfray, Ash, and Salter. The great mass of strata lying between has not fared so well, through several notice of it, to which I shall refer, have appeared. In the present paper I propose to describe these strata in detail; and the remarks I have to offer embody the results of three years' researches, during part of which I have had the advantage of the company and able co-operation of Messrs. Ezekiel Williamson and J.C. Barlow, whose discoveries I shall have to mention in my description of the rocks and their fossil contents. To facilitate the study of the district around Dolgelly, which is exceedingly faulted and complicated, I have carefully mapped out nearly the whole of the rock exposures. This may seem to have been unnecessary, seeing that we have already the Geological Survey maps of the district. But since the officers of the Survey examined and mapped out the rocks of Merionethshire, from fifteen to eighteen years have elapsed, and the maps which then added so much to our knowledge are now far behind our requirements.

For some years geologists have more or less agreed in the view that the present features of the earth, whether hill, valley, or plain (with some small exceptions, as volcanic outbursts) have been formed directly by denudation; though indirectly disturbances, whether faults upheavals or sinkings, have of course had their effect in determining the flow, so to speak, of the denuding agent.

Spirifer cuspidatus.—As I am somewhat committed to the opinion lately enunciated by Mr. Meek, that this species is characterized with a canal-system, I may be permitted to make a few observations on the subject.

The district selected for this article embraces a very unusual variety of geological phenomena, consisting of different kinds of recent gravels and Tertiary deposits, Greensand table-lands and patches, Triassic sandstone and conglomerate, rocks belonging to the interval between the Trias and uppermost Silurian strata, trap, and granite.

It is at all times difficult to fix the parentage of a new geological idea. So many circumstances and so many hints and observations converge to its establishment, when the due time comes for its appreciation, that, looking back, it seems hardly possible to disentangle the ideas of one workman in science from the suggestions of another. Hence it is always difficult to establish an exact priority of claim in questions which have remained long unsettled.

A Week or two spent last month at Llandudno has given me the opportunity of examining the deposits on the Great Orme's Head, described by the Rev. T. G. Bonney in the August number of the Geological Magazine, and supposed by him to be the remains of a Kitchen Midden. The present communication is intended merely as a supplementary note to his paper. It appears that the beds, containing recent shells and bones, had been previously observed, and their true character ascertained, since the Rev. W. S. Symonds remarks, in some notes on the Geology of the district, “The beds of mussels and other shells on the Great Orme, which, at one time I imagined to have been elevated in raised beaches, Mr. Darbishire believes to be derived from old shell-heaps the accumulations of former inhabitants.”

In the autumn of 1864, Mr. Ezekiel Williamson discovered fragments of trilobites in some slaty beds belonging to “Lower Lingula Flags” of the Geological Survey, on the right bank of the river Mawddach, a little above its junction with the Eden, and four and a half miles directly north from Dolgelly. Portions of an Olenus and of a Agnostus were found, but in too fragmentary a condition to be determined. Last summer Mr. J. Chamberlain Barlow, of Birmingham, found the same fossils in great abundance and good preservation on both sides of the Mawddach, opposite to Dolmelynllyn. During the present year I have, from these beds, added another species of Agnostus to the scanty fauna; and, after considerable trouble, in consequence of the rocks being greatly faulted, have Been able to determine the true position of this new fossiliferous zone.

It is well known that, though the Coal Fields of Lancashire and North Wales are now parted from one another at the surface by a broad tract of New Red Sandstone, there is reason to believe that the two are connected underground, and are bothparts of one and the same great deposit; and that the beds which in Lancashire and Cheshire dip out of sight below the Redmeasures, reappear in Flintshire and Denbighshire. Attempts have been made, I believe, to identify the individual coal-beds of the two districts, but I do not know with what success. During a short stay at Llangollen, some years ago, I venturedon a like task for the Lower Carboniferous Rocks, and though the time at my disposal allowed of only scanty observations, these were recorded in my note-book, in hopes that an opportunity might occur of filling in the sketch thus roughly tracedout. No such chance has befallen, or seems likely to befall me, and in the hope that the notes I then made may aid some one who, with more leisure, is willing to attempt a full solution of this problem, I now put them forward as a rough approximation.

The occurrence of “Sarsen-stones,” or blocks of so-called Druid sandstone, has not, I believe, been generally noticed in this locality, and their position may be of interest to some of your readers, more especially as the extensive working both for Brick-earth and Chalk have obliterated many of the interesting sections for which the pits were celebrated. Grays is well known both for its fine chalk-pits and extensive brick-earth deposits, the latter containing numerous remians of fossil mammalia, associated with land and fresh water mollusca. The sarsen-stones (of which some may be still seen lying about the large chalk-pit), I have noticed during the progress of the workings as occurring on the upper surface of a bed of disturbed chalk, above the solid chalk, and covered by a blackish or carbonaceous clay containing freshwater shells.

This well known genus of Old Red Sandstone Fishes was first named and described by Agassiz in his great work, the “Poissons Fossiles,” vol. ii. page 128. It is there classed with the Acanthodean family, which it somewhat resembles in the character and structure of its small rhomboidal scales; and also (according to Agassiz), in possessing Branchiostegal rays. This characteristic, however, as will afterwards be shown, appears to me to be founded on a misapprehension of the true nature of a series of elongated plates, situated below the lower jaw, which seem peculiar to this genus. The many points in which it very widely differs from the Acanthodeans induced the late Hugh Miller to suggest its removal altogether from them; and a distinct family, which he names Cheirolepini, is formed for its reception by Pander.

The recent deplorable explosions in the Barnsley and North Staffordshire Coal Fields have again called attention to the coincidence of such terrible accidents with a sudden fall of the barometer, by which they are so frequently preceded, suggesting the idea that they may be to some extent connected as cause and effect, and perhaps the following facts may induce a belief that there is truth in the supposition.

Some years since (in 1848) my attention was called to a well at Whittingham, on a farm then and now occupied by Mr. John France, about four miles N. W. of Preston, in Lancashire, celebrated in the district as “the blowing well.” This well was sunk for the purpose of supplying the farm buildings with water, but after going down about eighty feet in vain, the work was abandoned, and the well was covered with a large flagstone, with a hole through it for the chain used in placing it on the well.

The Graptolite which I am about to consider is perhaps one of the most remarkable of all our known British forms, and was originally described by Mr. W. Carruthers, under the name of Cladograpsus linearis. The genus Cladograpsus is one which was proposed by Geinitz to include certain forms of Didymograpsus; but Mr. Carruthers seems subsequently to have seen that the reference of G. linearis to this genus was inappropriate, as he has recently alluded to it, under the title of Dendrograpsus linearis.

The accompanying section shows the succession of beds from the Harlech grits, near the sixth milestone on the road from Dolgelly to Trawsfynydd, across their strike in a south-easterly direction, to the lower ash-bed of the Arenig group at the farm of Blaenau, five miles north-east from Dolgelly. In this section all the beds occur in regular sequence, although they are invaded by many intrusive masses and dykes of diabase; only the larger of which are shown in my section, as it would be impossible, on so small a scale to depict the innumerable protrusions of this rock that occur in the district. The section crosses, at Moel-Cors-y-garnedd, the southern flank of the mountain Rhobell-fawr, which is the largest mass of diabase in Wales. All along the eastern side of Rhobell-fawr the strata are completely inverted, as shown in diagram, so that the Festiniog beds (5 and 6) lie above the more recent Dolgelly beds (7 and 8), from underneath which the Tremadoc beds (9) come up, overlying the beds of slates and ashes belonging to the Arenig Group (10 and 11).

The Lower Silurian Rocks of the South of Scotland, below the level of the Wrae Limestone of Peeblesshire, though of great thickness, and little altered by igneous agency, have as yet yielded but few of the higher forms of animal life. Two species of a phyllopod crustacean, (Peltocaris aptychoides and P. Harknessi, Salter), were discovered by Prof. Harkness, along with the first Brachiopod found in these deposits, the Siphonotreta micula of McCoy. Another crustacean of an allied genus, described by Mr. Henry Woodward, and named by him Discinocaris Browniana, was discovered last year in the neighbourhood of Moffat, by Mr. D. J. Brown. Besides the above, there occur traces of the action of marine worms, and I have, in addition, found one, possibly two, species of Lingula, a thin-walled Orthoceras, or Pteropod, and some curious spine-like bodies, probably referable to crustaceans. With the exception of these scanty remains, the strata under consideration have yielded no fossils higher in the scale of existence than Graptolites. In no other British deposit do we, however, find a greater profusion of these beautiful and characteristic fossils, or a greater number of specific types. It is the object of this communication to describe certain new forms of Graptolites which have come under my notice, together with one remarkable genus, apparently allied to the Graptolitidœ, though probably representing a different order.

The specimen which I intend briefly to notice was obtained by Dr. Grindrod, of Malvern, about two years since, from the red, compact Sandstones, immediately resting on the grey ‘Passage-beds’ at Ledbury. Dr. Grindrod has kindly lent it to me for description.