fully sinking the tail, which was not insect-like, and for which no possible use could be discovered at the time-the Doctor succeeded in making the Pterichthys of Dura Den a very respectable beetle indeed. In a later publication, an Essay on the Geology of Fifeshire, which appeared in September last in the Quarterly Journal of Agriculture, he states, after referring to his former description, that among the higher geological authorities some were disposed to regard the creature as an extinct crustaceous animal, and some as belonging to a tribe closely allied to the Chelonia. Agassiz, as the writer of these chapters ventured some months ago to predict, has since pronounced it a fish-a Pterichthys specifically different from the five varieties of this ichthyolite which occur in the lower formation of the system, but generically the same. I very lately enjoyed the pleasure of examining the bona fide ichthyolite itself-one of the specimens of Dura Den, and apparently one of the more entire—in the collection of Professor Fleming. Its character as a Pterichthys I found very obvious; but neither the Professor nor myself was ingenious enough to discover in it any trace of the beetle of Dr Anderson.*

Is it not interesting to find this very curious genus

*This interesting ichthyolite has since been regarded by Agassiz as the representative of a distinct genus, to which he gives the name Pamphractus. As exhibited in his restoration, however, it seems to differ little, if at all (if I may venture the suggestion), from a Pterichthys viewed on the upper side. In Agassiz's beautiful restoration of Pterichthys, and his accompanying prints of the fossils illustrative of that genus, it is, with but one doubtful exception, the under side of the animal that is presented; and

in both the lowest and highest fossiliferous beds of the system, and constituting, like the Trilobite genus of the Silurian group, its most characteristic organism? The Trilobite has a wide geological range, extending from the upper Cambrian rocks to the upper Coal Measures. But though the range of the genus is wide, that of every individual species of which it consists is very limited. The Trilobites of the upper Coal Measures differ from those of the Mountain Limestone; these again, with but one exception, from the Trilobites of the upper Silurian strata; these yet again from the Trilobites of the underlying middle beds; and these from the Trilobites that occur in the base of the system. Like the coins and medals of the antiquary, each represents its own limited period; and the whole taken together yield a consecutive record. But while we find them merely scattered over the later formations in which they occur, and that very sparingly, in the Silurian System we find them congregated in such vast crowds, that their remains enter largely into the composition of many of the rocks which compose it. The Trilobite is the distinguishing organism of the group, marrying, if I may so express myself, its upper and lower beds; and what the Trilobite is to the Silurian formations, the Pter

hence a striking difference apparent between his representations of the two genera, which would scarce obtain had the upper, not the under side of Pterichthys been exhibited. In verification of this remark, let the reader who has access to the Monographic Poissons Fossiles compare the restoration of Pamphractus (Old Red, Tab. VI., fig. 2), with the upper side of Pterichthys as figured in this volume, Plate I., fig. 1, making, of course, the due allowance for a difference of species.

ichthys seems to be to the formations of the Old Red Sandstone; with this difference, that, so far as is yet known, it is restricted to this system alone, occurring in neither the Silurian System below, nor in the Coal Measures above.

I am but imperfectly acquainted with the localities in which the upper beds of the Old Red Sandstone underlie the lower beds of the Coal Measures, or where any gradation of character appears. The upper yellow sandstone belt is extensively developed in Moray, but it contains no trace of carbonaceous matter in even its higher strata, and no other remains than those of the Holoptychius and its contemporaries. The system in the North of Scotland differs as much from the carboniferous group in its upper as in its lower rocks; and a similar difference has been remarked in Fife, where the groups appear in contact a few miles to the west of St Andrews. In England, in repeated instances, the junction, as shown by Mr Murchison, in singularly instructive sections, is well marked, the carboniferous limestones resting conformably on the Upper Old Red Sandstone. No other system interposed between them.

There is a Rabbinical tradition that the sons of Tubal-Cain, taught by a prophet of the coming deluge, and unwilling that their father's arts should be lost in it to posterity, erected two obelisks of brass, on which they inscribed a record of his discoveries, and that thus the learning of the family survived the cataclysm. The flood subsided, and the obelisks, sculptured from pinnacle to base, were found fast fixed in the rock. Now, the twin pyramids of the Old Red Sandstone,

with their party-coloured bars, and their thicklycrowded inscriptions, belong to a period immensely more remote than that of the columns of the antediluvians, and they bear a more certain record. I have, perhaps, dwelt too long on their various compartments; but the Artist by whom they have been erected, and who has preserved in them so wonderful a chronicle of his earlier works, has willed surely that they should be read, and I have perused but a small portion of the whole. Years must pass ere the entire record can be deciphered; but of all its curiouslyinscribed sentences, the result will prove the same— they will all be found to testify of the Infinite Mind.

CHAPTER X.

Speculations in the Old Red Sandstone, and their CharacterGeorge, first Earl of Cromarty-His Sagacity as a Naturalist at fault in one instance-Sets himself to dig for Coal in the Lower Old Red Sandstone-Discovers a fine Artesian WellValue of Geological Knowledge in an economic view-Scarce a Secondary Formation in the Kingdom in which Coal has not been sought for-Mineral Springs of the Lower Old Red Sandstone-Strathpeffer-Its Peculiarities whence DerivedChalybeate Springs of Easter Ross and the Black Isle-Petrifying Springs-Building-Stone and Lime of the Old Red Sandstone-Its various Soils.

THERE has been much money lost, and a good deal won, in speculations connected with the Old Red Sandstone. The speculations in which money has been won have consorted, if I may so speak, with the character of the system, and those in which money has been lost have not. Instead, however, of producing a formal chapter on the economic uses to which its various deposits have been applied, or the unfor tunate undertakings which an acquaintance with its geology would have prevented, I shall throw together, as they occur to me, a few simple facts illustrative of both.

George, first Earl of Cromarty, seems, like his namesake and contemporary, the too celebrated Sir