293 



Royal Society : — 



UniversaUty. 



In the spirit of the following definition, it would appear that 

 the Silurian system is universal — that is, it overspreads the whole 

 earth more or less completely, — and that its component parts were 

 laid down in a proximate time, — statements approved by M. Barrande, 

 Bull. n. s. xii. 361. Definition: — ''A formation may he considered 

 to be universal when it occupies large and small areas in very many 

 parts of the earth, often remote from and even antipodal to each 

 other, when it is always of like stratigraphical relations, is com- 

 jposed of like inaterials, and contains numerous genera in common, 

 together with some representative and some identical species.'* 



In support of our application of this definition to the Silurian 

 system, the * Thesaurus ' exhibits the widest possible distribution of 

 its fauna — a fauna, it must be remembered, which is pure from ad- 

 mixture with that of any other epoch which might possibly have 

 been progressing at the same time. 



The * Thesaurus' contains many examples of the same species 

 being in twenty to twenty-five different countries, large and far 

 apart — the same creature or creatures marking the route from land 

 to land. 



Table B, drawn up under the inspection of Mr. Salter, presents 

 195 species common to regions very remote from each other, some 

 of them being antipodal — a fact which tells the more forcibly from 

 the tenacity with which a large part of Silurian life clings to locality 

 as well as to horizon. 179 species are common to Europe and 

 America. Sixty Silurian genera have been brought from South 



Table B. 



