BIGSBY PALEOZOIC ROCKS OF NEW YORK. 281 



roiis animals of high, organization and possessed of great strength 

 and activity. Species are most in number in Trenton Limestone, bnt 

 are elsewhere common, and present themselves in three groups of 

 Middle Devonian. In Wales they are met with on the same hori- 

 zons, but culminate in far newer strata — those of the Lower Ludlow. 

 The total number in Wales is 35, inhabiting 9 groups. In Kew 

 York their number is 40, met with in 9 groups also — another curious 

 coincidence. In Wales they never attain the vast size of those in 

 the Black-River and Niagara sections. In the latter I have seen 

 them 6 feet long. 



3. Cfhazy or Black-River Limestone. — An abundant and varied 

 fauna enlivens this section. Here we have the first Zoophytes. This 

 order pervades 11 Silurian and 6 Devonian sections in New York. 

 Numerous in Trenton and Onondaga Limestones and in the Hamilton 

 series, they are in still greater force in the Niagara rocks, just as 

 the Welsh Zoophyta are in the Wenlock rocks on the same horizon. 

 Three species of Crinoidea are seen in the Ohazy group ; and in all 

 probability more will be detected. None are met with in the Birds - 

 eye Limestone ; but there are 11 in the Trenton. In the Niagara 

 rocks 31 species appear, and of great beauty. From this last epoch 

 they diminish in numbers rapidly. James Hall, however, expects 

 soon to add largely to both these orders from the Upper Silurian and 

 Devonian of this basin. They are very numerous in the Enghsh and 

 Khenish horizons of the same date. The three great genera of 

 Brachiopoda, namely Leptoena, Orthis, and Atrypa, with the lesser 

 one, Orbicula, make their first apj)earance in Chazy Limestone, the 

 species not being numerous. Several of the 17 genera of Silurian 

 Brachiopoda of New York (Megalomus, Meganteris, Merista, Lepto- 

 celia, and Waldheimia) run very short courses ; but the others ex- 

 hibit great tenacity of life. In Wales 6 out of 19 genera are short- 

 lived. 



The genus Leptcena of New York has its greatest number of 

 species in Trenton Limestone, and diminishes slowly from that point 

 in the palaeozoic series both upwards and downwards. All this is 

 true also of the Welsh Leptcena. This genus is numerous and 

 varied in the Middle Devonian of New York. They inhabit 7 sections, 

 - — 9 species being in the Hamilton rocks, and 10 in the Chemung. 



The 50 Orthides of New York Siluria culminate in the Trenton ; 

 there is only one in the Chazy Limestone. In the course of 9 sec- 

 tions this genus mounts up into Upper Pentamerus Limestone, the 

 newest stratum of this system. As to the Devonian system, it is 

 most abundant in the Hamilton rocks, the species being six there. 



The 73 Airy pee of New York occupy 13 sedimentary groups ; but 

 they are most plentiful in the Trenton, Clinton, and Niagara and 

 the central groups generally. The succeeding species are either new 

 creations or derivatives from earher life -provinces. They enter the 

 Carboniferous system. The Chazy Limestone has only one Lamelli- 

 branchiate genus, the AmbonycJiia. Five of its 7 Gasteropodous 

 genera have short lives. The genus Murchisonia originates here, 

 and, taking the whole of the Silurian system in New York, gives us 



