XXVI. — Account of some Terraces, or ancient Beaches, in the Isle of Jura. 

 By Captain VETCH, Roy. Eng., M.G.S. 



[Read February 21, 1823.] 



XO those who speculate on the great general revolutions to which our planet 

 was subjected in the early stages of its existence, it cannot but be interesting 

 to contemplate any changes in the relative situations of land and water, which 

 can be shown to have taken place on a more confined scale, and at a later 

 period. Proofs of some such changes may, I think, be found on the western 

 coast of the island of Jura ; and if they have hitherto remained unnoticed, 

 this is to be ascribed, not to the indistinctness of the phaenomena which I am 

 about to mention, but to the uninviting aspect of that island, which seen from 

 the Paps, the highest point, and that to which every traveller would naturally 

 repair in the first instance, appears to consist entirely of vast continuous beds 

 of quartz ; a detailed examination of which would ill repay the toil and priva- 

 tions, under which alone it could be undertaken, where the surface is so 

 rugged, the accommodations so scanty, and the weather so precarious. 



My own attention was first drawn to this subject on the summit of Ben an 

 Oir, whence looking in the direction of Loch Tarbert, I observed a num- 

 ber of white patches, which I concluded, in the first instance, to be sheets of 

 water. The telescope undeceived me ; but being still ignorant of their true 

 nature, I determined to visit them. On closer inspection, they proved to be 

 blocks of quartz, lying upon six or seven terraces ; the lowest of which was at 

 the level of high-water mark, and the most elevated about forty feet above it. 

 The aggregate breadth of these terraces varied according to the disposition of 

 the ground ; where the slope is precipitous it may be a hundred yards, where 

 gentle, as on the north side of the Loch, three quarters of a mile from the 

 shore. 



Their extent, as far as I could trace it partly along the shores of Loch 

 Tarbert and partly north and south of its entrance, may be eight or nine 

 miles. 



Their base is generally naked rock ; but along the shore of Isla sound, and 

 thence northward as far as Loch Tarbert, a thick bed of alluvium * composed 



* Dr. M'CuUoch's remark, that there appear no alhivia in Jura worthy of regard, must be 

 received with this qualification. 



