Page:Quarterly Journal of the Geological Society of London, vol. 29.djvu/184

140 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 8, duced point, is that in the Elgin district the formation, which is made up of the two well-marked members the Cherty Rock of Stotfield and the Reptiliferous Sandstone, is altogether isolated, and its stratigraphical relations therefore undeterminable. I believe that I am supported in this conclusion by those who have made this district the subject of their most constant and careful study.

Under these circumstances a question of great importance arises — namely, whether this remarkable formation exists in any other district, where its relations may be the subject of more successful investigation by the geologist.

The beautiful Ross-shire section of the Old Red Sandstone, which exhibits in a series of cliff-exposures a conformable succession of beds, from the lower conglomerates of the Northern Sutor of Cromarty to the light-coloured sandstone of Tarbet Ness, has been described by Professor Sedgwick and Sir R. I. Murchison*, the Rev. J. M. Joass†, and Professor Harkness‡. The supposition originally put forward by Sir R. I. Murchison, that the highest beds of this section represent the Reptiliferous Sandstone of Elgin, appeared to derive great support from the interesting discovery of footprints in these strata at Portmahomack and Cambus Shandwick, which discovery was made in 1863 by the Rev. J. M. Joass and the Rev. George Campbell§.

But, in spite of this most valuable discovery, I cannot but regard this identification of the strata of Tarbet Ness with the Reptiliferous Sandstone as a very doubtful one. In mineral character the former much more closely resemble the light-coloured sandstones of Upper- Old-Red age both in Elginshire and Sutherland. Too much weight must not be attached to the presence of footprints, which might, indeed, have been occasioned by Amphibians such as we now know to have existed at as remote a period as that of the Lower Carboniferous. Professor Elliot some years ago discovered what were supposed to be footprints in the undoubted Upper Old Red Sandstone beds of Nairnshire. This circumstance was brought under my notice by Dr. Gordon, to whom I am indebted for so much assistance in the study of this question. The slab on which these markings are seen was presented by Mr. Stables, of Cawdor, to the Elgin Museum; but, from examination of a cast of them, both Professor Huxley and Professor Rupert Jones pronounce these markings to be of exceedingly doubtful origin.

The strongest circumstance, however, against the identification of the Tarbet-Ness sandstones with those of Elgin is the absence at the former place of that most remarkable, indestructible, and easily recognizable stratum, the Cherty Rock of Stotfield. When we consider the manner in which the two members of the formation are always associated in Elginshire, and the fact that the preservation of the sandstones from denudation appears to be in


 * Trans. Geol. Soc. 2nd Ser. vol. iii. part i.

† Quart. Journ. Geol. Soc. vol. xix. (1863) p. 506.

‡ Ibid. vol. xx. (1864) p. 437.

§ Ibid. vol. xix. (1863) p. 506.