BIGSBY PALEOZOIC ROCKS OF NEW TORK. 



271 



recently in the world's history. Some exceptions to this rule I have 

 met with without any regular search ; but they may arise from re- 

 currence, may belong to passage-beds, or the specimen may have 

 been transported in the dead state. They deserve notice because 

 they suggest the interesting idea of migration from older into newer 

 beds, and, in successive generations, from place to place, through enor- 

 mous periods of time. In the great freedom of Molluscan movements 

 in primaeval epochs, and in almost infinitely slow oscillations of 

 level, may be recognized the probable instruments of migration. 

 We might thus learn the true birth-place of species ; and a Bala or 

 Trenton Brachiopod be thus ascertained to be the ancestor of an 

 individual buried in the Wenlock or Niagara of India. 



Table XII. — A numerical List of the Recurrent or Non-typical Fossils 

 of the Silurian System of New YorJc. 



09 



CD 



o 



Silurian Sections 

 of 



New York. 



Total Fossil 



Appearances. 



Plantae. 



CO 



1— 1 



O 

 O 



i 



oi 

 "0 



•rH 



Q 





 Ph 

 



■^ 

 



B 

 pq 



g 

 







1 







GO 

 



Gasteropoda. 

 Cephalopoda. 

 Pteropoda. 



03 



a 





Feet. 



30 



40 



60 



100 



1000 



4 



240 



1200 



650 

 200 

 350 

 30 

 100 



700 



Upper Pentamerus Tiimestone 

 Delthvr. Sh. Limest 



25 

 60 

 19 

 14 











1 



6 



12 



6 



3 



2 



3 



15 



10 



2 

 1 

 3 



"i 



"2 



2 







1... 





1 



1 



11 



14 



13 

 6 

 6 

 8 

 36 

 32 

 3 



47 

 33 

 54 

 11 



9 



1 











Lower Pentamerus Limestone 

 Waterlime Grroup 











1 



"3 

 3 





1 



2 



1... 



1 







1 

 1 



3 

 5 

 3 

 1 



"2 



2 



Onondaga-Salt Group 



29... 

 40... 



180 - 





1 







Coralline Limestone of Schoh. 

 Niagara Rocks 



"1 



1 

 7 

 5 



1 

 1 



9, 







r Clinton Hocks : . . . 



141 



21 



? 1 



103 

 46 



256 



24 



65 



19 



6 





3 4 



\ Medina Sandstone 



1 



1 



[ Oneida Conglomerate 



Hudson -River Group 















2 

 1 

 3 

 2 

 1 



3 

 5 

 3 

 1 

 1 





 



3 



2 



1 



1 



14 



15 



16 



1 



1 



2 

 1 



5 

 1 



5 



"i 



6 

 3 

 13 

 1 

 1 



5 

 3 

 6 

 5 

 3 

 1 



6 

 3 

 3 





2 

 "2 



Utica Slate 



Trenton Limestone 



Birdseye Limestone 



Chazy Limestone 



2 







/ Calciferous Sandstone 



1 Potsdam Sandstone 

























































Total 



1048 







23 



17 



18 



103 



15 



13 



40 



31 



22 



1 



6 280l 











1 



Becurrence, we repeat, is a measure of the tenacity of life pos- 

 sessed by an animal — of viability, or a capacity for enduring 

 changes of food, shelter, temperature, and such-like. It is also the 

 measure of connexion and mineral similarity between strata. It 

 contributes a marked feature to all palaeozoic systems, being a bond 

 of union throughout a long chain of parts — a hving nexus, which, 

 beginning with the earliest sedimentary bed of the Silurian system, 

 passes upwards and combines the Silurian, Devonian, and Carboni- 

 ferous rocks into one vast whole. For the moment we leave the 

 Cambrian system out of consideration. Granting the great import- 

 ance of recurrence, we observe that the animals so endowed were in 



