264 Prof. Sedgwick on the Geological Structure 



group ends (as seen on the shore near Girvan) with a great 

 mass composed of greenish arenaceous slate in thin bands, 

 alternating with greenish bands of hard quartzose sandstone, 

 and occasionally with irregular beds of conglomerate, much 

 contorted here and there, but on the whole dipping N.W., at 

 a great angle. The beds last noticed are erroneously coloured 

 in M'Gjilloch's map as old red sandstone. 



(4.) North Girvan Group. — This last (and the author 

 thinks the highest group on the north flank of the chain) rises 

 from beneath the carboniferous rocks of Girvan water above 

 Dalquharran, into a rudely dome-shaped mass about three 

 miles long, and extends to a great concretionary and highly 

 inclined mass of limestone at Craig Head, which is near the 

 S.W. end of th^ group. This limestone is associated with, 

 and partly penetrated by, a great mass of trap ; and its struc- 

 ture is partly metamorphic, so that good fossils can only be 

 procured from its more earthy associated beds. The whole 

 group (to which the limestone seems subordinate) is overlaid 

 by trap rocks, by the carboniferous rocks of the coast of Ayr- 

 shire, and partially also by the conglomerates of the old red 

 sandstone. It seems also to be underlaid by indurated shales 

 and flagstones, which contain numerous trilobites. Its pre- 

 vailing character is, however, that of a shelly limestone, like 

 that which in South Wales separates the Llandeillo flag from 

 the tile-stone and the old red sandstone ; and this is the 

 geological place which the author gives it, both on what he 

 considers good physical and zoological evidence. 



(5.) Balmae Group. — Under this name is included a group 

 of rocks which, near Balmae farm, bound the S.E. extremity 

 of Kirkcudbright Bay. The group is essentially composed 

 of a hard, coarse, and thick bedded greywacke, alternated 

 with flagstone in thin bed?, and with thick masses of indu- 

 rated slate, containing septaria and other calcareous con- 

 cretions. In some of these beds are numerous graptolites, 

 and associated with the calcareous concretions were corals, 

 oi'thoceratites, and shells, both bivalves and univalves. The 

 fossils are not easy to procure ; but a good series submitted 

 to the Geological Society of London by Earl Selkirk was 

 collected by Messrs Underwood and Fleming, and they ap- 



