President's Address. 9 



have disappeared in Cambrian or early Silurian time, but 

 has now been proved to be a common Devonian fossil, forms 

 another example of the danger of founding conclusions on 

 purely negative evidence. 



The passage beds between the Upper Silurian and Lower 

 Old Eed Sandstone formations in the south of Scotland pre- 

 sent certain features of special interest to the palaeontologist. 

 The greatest development of Upper Silurian strata in Scot- 

 land extends along the border from the Cheviots to Burrow 

 Head, but at present I propose to confine my attention to 

 the exposures of these rocks in Lanarkshire and the Pent- 

 land Hills. In the area of Upper Silurian rocks at Les- 

 mahagow, about 4000 feet of greywackes and shales are 

 conformably overlain by a succession of red marls and con- 

 glomerates marking the lowest beds of the Old Eed Sand- 

 stone. A similar passage is met with in the anticlinal axis 

 of Upper Silurian rocks in the Hagshaw Hills, and also in 

 the Pentland area. The highest Silurian strata in these 

 separate areas consist of greenish and grey sandstones, shales, 

 and greywackes, containing a peculiar assemblage of fossils. 

 These beds are the great home of the Eurypterids. Indeed, 

 the strata in the Lesmahagow area are widely known on 

 account of the numerous species obtained from them, which 

 have been described by Huxley, Salter, and Woodward. The 

 passage beds from the Ludlow formation to the Hereford 

 type of the Lower Old Eed Sandstone in Shropshire have 

 ahbrded numerous fragments of Eurypterids nearly allied to 

 those of Lesmahagow, while the other included fossils closely 

 resemble those from the same horizon in Scotland. To- 

 wards the top of the Upper Silurian formation in America, 

 in the Water-lime group, Eurypterids are also abundant. 

 Now, I venture to think that the occurrence of the Ludlow 

 facies of fossils in these widely-separated areas does not point 

 to contemporaneous deposition. In my opinion, this remark- 

 able group of fossils represents the shallow-water and shore 

 animals of the Silurian sea. Were older Silurian land sur- 

 faces and shore deposits to be found, they might be expected 

 to yield a similar fauna, though the species would in all 

 probability be distinct. The occurrence, therefore, of the 



