﻿« 



1851.] MURCHISON SILURIAN ROCKS OF SCOTLAND. 149 



In the meantime, with reference to the 

 Saugh Hill section (fig. 2), it may be noted, 

 that in some of the courses of its sandstone 

 there occurs a band so shelly as almost to 

 be called a bastard limestone, in which the 

 Pentamerus oblongus is abundant. This 

 shell is associated with Tentaculites orna- 

 tus, Sow., Atrypa hemispheric a, Sow., and 

 Terebratula serrata, M'Coy. I attach im- 

 portance to the abundant presence of the 

 Pentamerus oblongus, Sow., in association 

 with Phacops Stokesii, Tentaculites, and 

 other types, as marking, in Saugh Hill, an 

 upper portion of the Lower Silurian rocks. 

 For, although I have been informed by Mr. 

 Salter and the Government geological sur- 

 veyors, that they have also found abun- 

 dantly the Pentamerus oblongus deep in the 

 Lower Silurian, still I am of opinion that its 

 most usual position (certainly the Phacops 

 Stokesii belongs to an upper stratum) is 

 as above stated. I therefore hold, that in 

 this transverse section across Saugh Hill 

 (fig. 2), the Lower Silurian rocks with fos- 

 sils (2) indicate an ascending series, and 

 form the sides of a trough on which or- 

 thoceratite flagstones (1) repose. Other 

 proofs of this order follow. 



Conglomerates, Orthoceratite Flagstones, 

 and Graptolite Schists of the Coast Sec- 

 tion south of Girvan. — Turning from the 

 inland transverse section just described, to 

 the coast, the geologist, who knows how 

 rarely he can trace the true Silurian order 

 in any sea-cliffs and ledges of the British 

 Isles, is not altogether disappointed. But 

 unluckily, in commencing the section from 

 Girvan, and in proceeding southwards, he 

 meets with no trace of the shelly sand- 

 stones, so abounding in fossils in Saugh 

 Hill and particularly on its northern slopes. 

 They are all denuded. In following the 

 strike of these beds from Saugh Bill until 

 we reach the coast, they are there found to 

 be rounded off and obscured ; and all the 

 shore in which, according to their strike, 

 they ought to appear, is simply a sandy 

 beach (see fig. 3). This may be accounted 

 for by the fact, that these shelly sandstones, 

 where they are not in the vicinity of igneous 



