Crossing the railway to the harbour, a footpath brings us to some old white-washed cottages, “The Folly Houses,” as they are called (but why I know not), where a young dealer (Griffiths) lives, of whom some good specimens may often be got. Continuing the footpath to the edge of the cliff, we descend by rugged green-sand steps again to the favourite collecting ground, Eastwear Bay.

Slowly the bright green tide is quitting the flat shore, and leaving again exposed the dark blue clay, dotted with black phosphatic nodes and glittering iridescent shells, washed clean and bright. Daily may you pick up hundreds of these ancient inhabitants of the sea; gather the crop as clean as you will, there will be another harvest for you when the next tide falls. Here are Inocerami, or “fibre-shells,” in abundance. Two species, the Inoceramus sulcatus and Inoceramus concentricus—the furrowed and concentric are particularly characteristic of the gault.

Opercula of Ammonites are common in many localities, especially in banks and sections of the Kimmeridge Clay; but they usually occur in broken fragments, and very rarely with their valves paired, unless sheltered within the last whirl of the shell to which they belonged. Even when thus protected the valves are generally displaced, as might be expected if we consider how slight is their union along the suture, and how great were the chances of being shifted by the contraction of the animal after death, by the pressure of external mud.

The British Museum contains several examples of Ammonites Jason, A. Brightii, A. fluctuosus, A. lingulatus, and other species with their opercula more or less shifted; and Mr. Charles Moore, of Bath, has several small shells of Ammonites planorbis from the Lower Lias, with the opercula remaining in their true position; the smallest individual is only one quarter of an inch in diameter.

On examining the interior of the pipes, I have invariably found the surface to be more or less decomposed. For about half an inch—sometimes less and sometimes more—the texture and hardness of the limestone is completely changed—so much so that it is possible to scrape it away with the finger-nail. This is the case with all the beds, no matter how they may differ in texture and general character, though some seem more affected than others. This alteration is best seen in those strata that are crystalline. In one part of the quarry is a bed of which the limestone is hard and dolomitic, and also finely laminated, there being more than a dozen laminæ to the inch; this is its normal character, but where it is penetrated by a pipe it looses its hardness, and becomes dull and earthy; the laminæ also, which in the unaltered portion of the pipe are firmly coherent and difficult to separate, are here easily split open, the surfaces of their planes being highly decomposed; the colour, too, of the decomposed portion is somewhat changed, being of a light yellow, while tho limestone of the bed generally is of a brown or grey hue, and so soft has it become where it forms the surface of a pipe that it crumbles to pieces on being touched, and for half an inch in it can be cut with a pocket-knife.

As anything calculated to throw light on the peculiar fauna of the Old Red Sandstone period must be interesting to geologists, I send you a short notice of some fossils lately found in the flagstones of Forfarshire, which may aid in adding to our knowledge of the peculiarities of the creatures found in these rocks.

Some six weeks ago, by far the finest specimen of Pterygotus anglicus yet found was discovered in the “pavement” quarries of Cannyllin: this superb specimen is now in the Arbroath Museum. This fossil, coming clean out from the matrix in which it was imbedded, consists of all the body-segments, a part of the caudal plate being also preserved and well seen in the cast from which the fossil had been lifted. It shows no features absolutely new or hitherto unknown, but it is nevertheless very interesting, as exhibiting the manner in which both the dorsal and ventral portions of this creature had been covered and protected by strong sculptured plates. It also proves that Mr. D. Page was quite correct in the place which he latterly assigned to the curious duck-bill like plate with its wing-like appendages, which, as noticed in Hugh Miller's “Old Red Sandstone,” occasioned the name of “Seraphim” to be applied to this fossil. It is found in situ, covering the under portions of the segment next the head. In all probability, as suggested by Mr. Page, it formed part of the sexual organs of this creature, and also a covering for the vent or anal opening, there being no vestige of any such opening in either the sub-caudal segment, in the portion of the caudal plate, or telson, preserved, or on the junction of these segments.

Having at times been asked questions about the “Fossiliferous Ironsands” of the North Downs, which Mr. Prestwich described in the Journal of the Geological Society in 1858, vol. xiv., p. 322, &c., I find that some little diagram appears to be wanted by amateur geologists and general readers for the clearer demonstration of these strata and their relations to the Chalk and the Drift.

I beg, therefore, to offer you the accompanying diagram, illustrative of the relationship of the so-called “Kentish Crag,” agreeable, I believe, to Mr. Prestwich's views of the subject, as given in his elaborate paper before mentioned. Having seen the ground at Lenham and Charing, to which Mr. Prestwich refers, and at the latter of which places my friend Mr. W. Harris, F.G.S., had some sections specially made, I feel the greater satisfaction in bearing testimony to Mr. Prestwich's careful working out of the whole question.

In the foregoing account it has been my aim and endeavour to describe the geological formations in which the caverns existed; this will be seen at a glance in the following table:—

Taking the two classes together as representing thirty distinct series of cavernous localities, one is found in the New Red Sandstone formation, two in the Carboniferous, two in the Devonian or Old Red, seven in the limestones of the Upper, two in those of the Middle, and six in those of the Lower Silurian formation, three in the Huronian rocks of Sir William Logan, and seven in the Laurentian rocks of the same geologist. In the last of these they are present in the interstratified bands of crystalline limestone, characteristic of this formation in Canada.

To the thick-skinned quadrupeds belong animals of at least four genera—Elephant, Rhinoceros, Horse, and Hog.

In addition to the large grinders of the mammoth, before described, there occurred a remarkable molar tooth of a very young mammoth (length or anteroposterior diameter of the crown one inch and three-quarters, breadth one inch and one-eighth), containing six plates; it appears to belong to the “thick-plated” variety, but is unlike any of the numerous small grinders of this animal, contained in the British Museum and elsewhere, with wnich it has been carefully compared.

The larger molars of the rhinoceros were all fragmentary; but a small tooth, having its enamel equally thick with that of the larger specimens, may, it is presumed, belong to a small species of that animal.