TRANSACTIONS OF THE SECTIONS. 645 



Connected with the sandstone flag we find thick beds of com- 

 mon sandstone, of a yellowish or tile-red colour. It forms the 

 chief part of the momitains of Hoy, the highest point in Ork- 

 ney ; and also several headlands in Pomona and in Edey. In 

 the vicinity of the red sandstone we occasionally find the strati- 

 fied flag assuming a higher inclination. 



Last year Dr. Traill discovered a thicker bed of basalt in the 

 sandstone of Hoy; and there are many veins of basalt and 

 greenstone traversing the slaty rocks, particularly in Shapin- 

 shey, and in that part of Pomona where the fossil fishes are 

 found. It may not be unworthy of notice, that the general di- 

 rection of these last trap veins is towards that part of Hoy in 

 which the bed of basalt occurs. 



Granite exists in Orkney only in one district. It constitutes 

 a chain of moderate hills, running from the southern boundary 

 of the township of Yesnaby, in a south-east direction, to Strom- 

 ness ; occupying a length of about six miles, with a breadth 

 varying from one to half a mile. The granite again appears on 

 the north side of the small island of Grsemsey; biit the slaty 

 rock is interposed between it and the mountains of Hoy. This 

 granite is close-grained, contains much felspar, and often ap- 

 pi'oaches to gneiss in structure. 



The granite is everywhere in immediate contact with a coarse 

 conglomerate, consisting of nodules of quartz, and fragments of 

 granite and sandstone, imbedded in an arenaceous base. The 

 junction of these rocks is well seen at the western end of 

 Graemsey, on the shore at Stromness, and in the burn of Cairs- 

 ton. The conglomerate is of small extent, almost immediately 

 passing into sandstone flag. Both the granite and the conglo- 

 merate bear a striking resemblance to the prevailing rocks on 

 the eastern side of Sutherland and the south of Caithness; 

 and the sandstone flag of Orkney is so exactly similar to the 

 slaty rock of the latter county, which also contains fossil fishes, 

 that it is impossible to resist the conclusion, that these rocks 

 belong to the same geological epoch. The researches of Messrs. 

 Sedgwick and Murchison have proved that the Caithness flag 

 is a member of the old red sandstone ; repeated observations, 

 and an examination of most of the Orkney Islands, have con- 

 vinced Dr. Traill that the sandstone and sandstone flag of that 

 group ought to be referred to the same formation. In no part 

 of these islands did he discover any traces of a coal formation, 

 unless, with some geologists, we are to consider the slaty rock 

 charged with bitumen as the lowest bed of that deposit; for 

 certainly no vestige of its other more important members exist* 

 in Orkney. 



