Tlie Old Red Sandstmie of Orkney. 329 



VIII. Tlie Old Red Sandstone of Orhmj. By B. N. Peach, 

 Esq., r.G.S., and John Horne, Esq, F.G.S. [PL XVIII.] 



(Read 21st April 1880.) 



While engaged in working out the glacial geology of 

 Orkney, during our leave of absence from official work, 

 in the autumn of 1879, we had occasion to pay some atten- 

 tion to the geological structure of the Old Eed Sandstone, 

 which is so largely represented in that group of islands. 

 In the course of our traverses we detected certain points 

 regarding the physical relations of the strata which have not 

 as yet been described; and we likewise noted a new and 

 interesting feature in the history of this formation in Orkney, 

 viz., the proofs of contemporaneous volcanic action in Lower 

 Old Eed Sandstone times. In the paper now laid before the 

 Society we purpose to describe briefly the general results of 

 these observations. 



The abundance of ichthyolites in the flagstones of Orkney 

 was made known through the descriptions of Agassiz, and 

 more recently by Hugh Miller in his well-known volume 

 " The Footprints of the Creator." In the opening chapters 

 of that work he makes the following statement : 



" It is not too much to affirm that in the comparatively 

 small portion which this cluster of islands contains of a 

 system regarded only a few years ago as the least fossiliferous 

 in the geologic scale, there are more fossil fish inclosed than 

 in every other geologic system in England, Scotland, and 

 Wales, from the coal measures to the chalk inclusive." 



In spite of the inducement herein contained, the ichthyo- 

 logy of Orkney has never been so vigorously or exhaustively 

 worked out as that of Caithness and the Moray Firth basin. 



The paper published by Sir E. Murchison in the Quart. 

 Jour, of the Geol. Soc* contains a brief description of the 

 geological character of the deposits, and an attempt to cor- 

 relate the strata with the representatives of the same forma- 

 tion in Caithness. He refers to the axis of ancient crystal- 

 line rocks near Stromness on which the Lower Conglomerate 



* Quart. Jour. Geol. Soc, XV., 410. 

 VOL. V. Y 



