236 TRANSACTIONS, NATURAL HISTORY SOCIETY OP GLASGOW. 



fossils nor adding a single stroke to the picture furnished to 

 us by the geologists named. However, " instincts will out," 

 and one day, in passing up the Cleuch (the second one on the 

 right side of the head of the Snar Valley) that comes down 

 from Hunt Law, I came in face of a small cliff of radiolarian 

 chert, the bands of which had been slightly parted asunder by 

 the frost. The thin layers of shale between the chert could be 

 picked out by the fingers, and, as they seemed to have been 

 prepared by Nature for microscopical examination, I took a 

 few, and, after washing and preparing them, I found on their 

 surfaces abundance of Conodonts. There would be about one 

 to every square inch of surface, sometimes as many as three 

 on that area of the shale, which could be easily split into 

 laminae a sixteenth of an inch thick, or even thinner. I was 

 now in an assured position to carry out an extensive micro- 

 scopical examination of the chert-shales and other deposits of 

 the Silurian Rocks of the South of Scotland, and with this 

 object in view I spent a considerable time in collecting material. 



The shales of the Silurian formations of the Southern Uplands 

 and the Ayrshire coast sections (other than those intercalated 

 in the chert beds), with four excej^tions, to be referred to in 

 the sequel, I found to be utterly devoid of Conodonts. These 

 shales are of various shades of grey, green, and red, and few of 

 the larger fossils occur in them. The presence of mica in them, 

 after it reaches a certain proportion, seems to have been inimical 

 to life or to fossil preservation. Even in the black shales, which 

 often contain abundance of Graptolites and hingeless Brachiopods, 

 I found no Conodonts, and some of them are pretty fine grained. 



The exceptions already referred to are, first, a bed of shale 

 which occurs close to a chert-shale bed, and contains abundance 

 of Conodonts, occasional Graptolites, and hingeless Brachiopods. 

 The mica in this shale is abundant, but in minute white scales, 

 and from what I have seen of other shales I think I may safely 

 say that, had the particles of mica been a little larger, this 

 bed would also have been without Conodonts. 



The second is the thick bed of Indian-red Arenig Shale well 

 seen at several places in the Southern Uplands. I first made 

 my acquaintance with it at Morroch Bay, on the west coast of 

 the Mull of Galloway, where a complete exposure of a thick bed 



