DR TRAILL ON FOSSIL FISHES FOUND IN ORKNEY. 91 



The whole of that group, with these exceptions, consists of rocks which I consider 

 as belonging to the old sandstone formation. 



As it is important to determine the geological position of these fishes, I shall 

 here give an abridgment of my notes on the geology of Orkney. 



In this formation, massive sandstone, both red and yellowish, occurs in Hoy, 

 in Edey, at Holland-head and Getnip in Pomona. The principal rocks in all those 

 islands is a distinct sandstone-flag. In two or three points, as at Yesnaby in Po- 

 mona, and at How in Shapinshey, thin beds of limestone occur ; and at several 

 places the sandstone-flag passes into a slaty-clay, occasionally impregnated with 

 bitumen, as near Skaill, at Yesnaby, in Walls, and in the rock of Ruskholm, off 

 Westrey. The rocks are in some places intersected by trap-dykes. The largest 

 of these occurs in Hoy, opposite to Stromness : Several are found along the coast 

 from Breckness to Skaill, and in Shapinshey, on its southern shores, and at Long- 

 hope in Walls. From this sketch it will be seen that the geological formation of 

 Orkney is very simple and little varied. 



The granite ridge on its eastern side appears here and there to pass into 

 gneiss, and in one point I observed a limited extent of mica-slate ; but in the 

 greatest part of its course, the rock immediately in contact with the granite is a 

 conglomerate with a sandstone base, containing fragments of these primary rocks! 

 This conglomerate passes by insensible shades into sandstone-flag, which has often 

 a dark iron-grey colour, from containing bitumen and oxide of iron. 



It is between the layers of this sandstone-flag that the fossil fishes are found, 

 where it is quite schistose, and in fact is quarried in large slabs, varying from half 

 an inch to twelve inches in thickness. The fossil fishes at Skaill do not occur in 

 the upper layers of this rock. I observed in the quarry about three feet of soil 

 and debris of the rock, then nine feet of solid stone-beds ; and below these two 

 other thick beds of flag, in which the fishes are found. This was the lowest point 

 to which the quarry was wrought at the period of my visits in 1833 and 1834. I 

 found, in the same beds with the fishes, a few fossil plants, which seem to be 

 Algse or Fuci. 



From geological position, from its connection with the massive sandstone, 

 and its vicinity to the granite ridge, I consider this flag to belong to the old sand- 

 stone formation ; which is confirmed by its identity with the Caithness flag in 

 appearance and in fossil remains. In fact, the organic remains would indicate 

 that this flag is very low in the series of that formation. Since 1834, fossil fishes 

 have been found in several other parts of Pomona. They are no less numerous 

 at Breckness, six or seven miles farther south than Skaill ; and fine specimens 

 have more lately been found in a quarry at Quoyloo, a mile to the north of the 

 first locality : I found scales, which I now consider as those of Platygnathus, near 

 Kirkwall, a distance of fourteen miles east of that point : Very fine specimens of 

 fossil fishes have also been found in the same species of flag at Hoxahead in the 



