BIGSBY PALEOZOIC EOCKS OF NEW YORK. 293 



many or few. 9. The great majority observe the same process or 

 law of increment and decrement. This takes place in nineteen out 

 of twenty-four orders and genera. 10. The two basins have 108 

 organic forms in common, including most of the genera. 11. The 

 same orders and genera are rich and poor in species. 12. There 

 is the same limited admission of Silurian forms into the Devonian 

 system in New York and in Europe. 13. The plants of both are 

 typical, with one or two exceptions. 



Such are some of the great points of similarity. Now as to dissi- 

 milarity. Those which arise out of the mineral character are 

 partly owing to physical disturbances and to a certain amount of 

 metamorphism undergone by the Welsh strata. The palaeonto- 

 logical differences are many, but small, often merely individual ; and 

 they seldom affect principles. They are due to the varying sea- 

 depths and other well-known conditions. 



The facts just recorded certainly indicate a close connexion, in 

 nature and mode of formation, between the basins of New York and 

 Wales, They seem to be quasi- equivalents — '^ the same, but other," 

 to use a short and convenient phrase in common use. 



This near approximation is the more surprising, when we consider 

 under what very different circimistances the two sets of deposits 

 were thrown down, and, further, that the nearest neighbours to the 

 Welsh basin on the south-east and north-east are so different from 

 it, as we see in France, on the E-hine, in Saxony and Spain — 

 countries, which, among other differences, have often no Upper 

 Silurian. 



We seem therefore led, by analogies in other branches of natural 

 history, to the reasonable and very interesting suggestion, that pro- 

 bably in early palaeozoic times the eastern and western hemispheres 

 communicated between the latitudes 42° and ^2°, either by dry land 

 or a shallow sea. This space would include western Europe, from 

 Sweden (full of Welsh fossils) to the south of Erance, and of course 

 Great Britain and Ireland, on the one side, and the State of New 

 York, with Canada, on the other. We should then be able to 

 account for the intimate relations existing between these two palaeo- 

 zoic areas, according to the laws of animal and vegetable progression 

 from land to land. 



I feel constrained to yield a waiting belief in a former continuity 

 of land between New York and Great Britain, for the following 

 reasons : — 



That such continuity did exist at this epoch, the State Geologists 

 of New York have inferred from the distribution of its conglomerates, 

 grits, sandstones, clays, and Kmestones — those of the Middle and 

 Upper Silurian periods especially. This distribution, together with 

 the vestiges of certain currents impressed on rock-surfaces, appears to 

 them to indicate the removal of large spaces of land from the site 

 of the present Atlantic Ocean into the eastern and middle portions 

 of North America. We draw the same conclusion from the quasi- 

 equivalency of our two areas, as above shown. 



Sii' E. Murchison states, that there is at Durness, in Sutherland, 



