18(J9.] The Treasures of Siluria. 37 



well known), 784, or 13 per cent., are recurrents, leaving 5184 

 faithful to one horizon. But this statement does not describe the 

 scope and value of the table, which may be epitomized as follows : — 

 In the Lower Silurian rocks 354 species occur on two horizons — 98 

 on three, 44 on four, and 5 on five. In the Middle Silurian 95 

 species occur on two horizons — 29 on three, and 3 on four. In 

 the Upper Silurian 138 species occur in two divisions, 15 in 

 three, and 3 in four. 



There are many curious facts connected with recurrence, several 

 of which are not yet properly understood. In one region a species 

 may be restricted to one horizon, being there traly typical, while in 

 another region the same species may pass through nearly the whole 

 of the subdivisions of the Silurian series. Speaking generally, 

 recurrence is common in Sweden and Canada, and still more so in 

 Wales. It is rare both in Kussia and Bohemia. In the last-named 

 country we have seen that species of short duration and belonging 

 to a small number of genera are extremely abundant. Surely this 

 contrast is another fact in favour of the views we have already 

 advocated. 



After reading through the " Facts and Observations," we at 

 j&rst felt somewhat uncertain as to the author's views on the 

 important subject of Contemporaneity of Strata. He does not say 

 much about it; and, with the exception of the first and last 

 sentences which we quote below, his statements do not help us 

 very powerfully to a conclusion. 



(1.) '"We already have materials fi-om almost all parts of the 

 Silurian scale of rocks to show, with some force (M, Barrande), that 

 life began earlier and more abundantly in the valleys of the St. 

 Lawrence and Mississippi than in Europe." * 



(2.) " It would appear that the Silurian system of rocks, is 

 universal in extent, and that its component parts were laid down 

 at a proximate time, and in like manner ceased to be laid down, 

 statements approved by M. Barrande." f 



(3.) "It is a very striking fact that the great majority of the 

 Silurian fauna made their first appearance on the same horizon — • 

 that is, everywhere on, proximately, the same stage or subdivision 

 of the epoch." :|: 



(4.) " Silurian life was discontinued everywhere at the same 

 time, proximately." § 



(5.) " The Upper Silurian fossils which people the Prague 

 colonies in fauna D.d, except as they come from another area, are 

 not recurrents, are not the posterity of Bohemian mollusks. They 

 are the lorecursors of an identical and larger coming fauna. Signs 

 are not wanting that they come from a country ivhcre the Silurian, 



* P. xi. t P- xxxiii. % P. xxxvii. § P. xl. 



