During a visit to the Giant's Causeway in the month of September, 1857, I made a few notes and sketches on the spot, having reference more particularly to the determinating of the stratigraphical position of the Causeway itself, and to get if possible a clear idea of the structure of the exposed cliff-sections of the basalts in the immediate neighbourhood. On comparing my observations with an account of the causeway and the adjoining coast given by the Rev. John Dubourdien in his statistical survey of the county of Antrim in 1812, I was struck with the discrepancies which exist between them, the author's idea being that the bed of Basalt forming the Causeway extended eastward to Portmoon, a distance of two-miles (page 46), and that the whole of the strata are parallel to each other. These suppositions are, as far as I am aware of, adopted by all subsequent writers on the Causeway; and as they are errors, a transcript of my notes may not be unacceptable to the readers of the “Geologist;” they tend at least to illustrate more fully the structure of the Basaltic deposits to which I allude, and are a few additional facts added to our present information on this interesting subject.

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.

The greater part of the main road from Carillon to Grenville, a distance of thirteen miles on the northern banks of the Ottawa River, runs over the Calciferous sand rook of the Lower Silurian formation. In many places ihe surface of the rock is exposed, and beyond the village of Chatham, towards Grenville, and even in Chatham, for a short distance, the road consists of the solid limestone rock. As the surface of the rock is more or less rough or uneven, the road is an uncomfortable one to travel over in a wheeled vehicle. On driving over that part of the rock just near Chatham, a tremendous loud rumbling noise is occasioned by the stage, which is not heard, in other situation. This has been attributed to the presence of one or more large caverns situated beneath the road at this place: and, on making inquiry on the spot, I learnt that a prevalent opinion has long been entertained by the country people and many intelligent persons in the to neigbourhood, that a considerable cavern does exist in this part of the country in the place mentioned. On the many occasions that I have driven over this road, the loud rumbling noise has been invariably observed by my fellow travellers as well as by myself. Sotne-day an opening into the cavern may be discovered and the mystery solved. The main road is, elevated and is probably from seventy to ninety feet above the level of the Ottawa River.

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.

The shells composing this species vary but slightly in shape, being marginally semicircular, concavo-convex, and about one-third wider than long. The hingeline is straight, and either a little shorter, with its cardinal angles rounded, or somewhat longer than the greatest width of the shell, with rectangular or slightly acute and extended terminations. Both valves are provided with narrow sub-parallel areas, the ventral one, which is the largest, being divided by a small fissure, partially covered with a pseudo-deltidium; while in the middle of the ventral one there exists a prominent V-shaped cardinal process. The ventral valve is moderately convex, and flattened towards its auriculate cardinal extremities. The beak, which is small and incurved, does not overlie the hinge-line; while the dorsal valve assumes in different specimens a greater or lesser degree of concavity, and follows the curves of the opposite one. Exteriorly the surface of the ventral valve is covered with numerous small thread-like radiating striæ, which increase in number by occasional bifurcation, or interstriations at various distances from the beak, so that as many as one hundred and twenty ribs may be counted round the margin of certain specimens, while at irregular distances small spines projected from the rounded surface of the striæ. In addition to these, on each side of the beak there exists along the cardinal edge from five to nine slanting tabular spines, which become longer and larger as they approach the extremities of the cardinal edge. The surface of the dorsal valve is striated as in the ventral one; and minute perforations or punctures may be perceived over the entire surface of the shell, and which are the exterior orifices of the canals which traverse the shell, as in Productus.

The shells of which this genus is composed differ much in their external shape and appearance, hence the great difficulty of correctly determining the limits of certain species. The character of this extinct genus are now so well understood that it is scarcely necessary to make any further allusion to the subject; but we may briefly repeat, for the sake of the less initiated, and in order to shorten the descriptions of the various species, that all possess a straight hinge-line, and a triangular or sub-parallel area, which is divided by a triangular fissure, this last being more or less covered, or contracted, by the means of one or two curved plates, to which the term pseudo-deltidium has been applied. The pseudo-deltidium is rarely preserved in the carboniferous specimens, but did certainly exist in the perfect or living individuals. The valves are articulated by the means of curved teeth developed on either side of the fissure in the ventral valve, and which fit into corresponding sockets in the opposite or dorsal one. In the larger valve the teeth are supported by vertical plates of greater or lesser dimensions, and in the space between these on the bottom of the shell are situated the muscular impressions. The adductor, or occlusor muscle leaves a narrow mesial oval-shaped scar, and on either side are situated the cardinal, or divaricator muscular impressions. In the interior of the smaller, or dorsal valve there exists two large conical spiral coils, which nearly fill the interior of the shell, the ends being directed outwardly towards the cardinal angles, while the bases of the hollow conical spires nearly meet at the hinge side, but are wide apart in front.