278 L. Agassiz on the Primitive Diversity 
proximate. I hope this general statement may meet your 
present requirement, but I regret that I cannot now give you 
more definite information, particularly regarding the Upper 
Helderberg. I give you from this and the higher groups an 
estimate based on the species known to me at the present 
time ; but my final pannetigations always reveal a greater 
number than [ anticipate.” 
These statements of Professor Hall place arial each of 
the principal group of rocks of the state of New York in the 
category of distinct independent successive faune, equivalent 
each to as many local faune of the present period, for we 
may repeat that the fauna of the Sechelles contains only 258 
Species, and that of Mauritius, Bourbon, and Madagascar, 
275. Nay, upon 3000 miles of coast along the western 
shores of the American continent, within the tropics, only 
twice the number of living species have been obtained as occur 
respectively in each successive greater subdivision of the 
paleozoic system within the narrow Jimits of the state of New 
York only.—(See above the results of Professor Adams’s in- 
vestigations upon the coast of Panama). 
It is a most unexpected and very significant coincidence 
that the late admirable investigations of Elie de Beaumont 
upon the mountain systems have led him to the recognition 
of nearly ten times as many periods of great disturbance in 
the physical constitution of the earth’s surface as he himself 
knew twenty-five years ago, each attended by the upheaval 
of as many mountain chains, differing in their main direction. 
The investigations of palzontologists having an entirely dif- 
ferent character, and founded upon facts which until recently 
have apparently had only a remote connection with the other 
series of phenomena, have nevertheless brought them at about 
the same time to like conclusions respecting animal life, 
showing that the periods of disappearance and renovation of 
organized beings upon earth have been much more frequent 
than could be supposed even ten years ago, each set having 
probably been‘ characteristic of one of those long periods of 
comparative rest, intervening between two great successive 
geological cataclysms. 
What is true of Mollusca, may be said of all other classes. 
