BIGSBY PALEOZOIC ROCKS OF NEW YORK. 291 



species of Lamellibranchiata, and of BJiynchonella and Terehratula 

 among the Brachiopoda, range through the subdivisions of the 

 Oolitic series. He also mentioned to me the circumstance, that the 

 Iguanodon and Lonchopteris of the Wealden are found in the Lower 

 Greensand. The assumed law of Agassiz is still further disproved 

 by the graduated disappearance of Tertiary animal life, upon which 

 Sir C. Lyell has based his beautiful classifications ; and the same 

 occurs in the vegetation of the Tertiaries, according to M. de la 

 Harpe, as quoted in our President's Address for 1857. Mr. David- 

 son tells us that 3 species of tertiary Brachiopoda (Terehratula caput- 

 serpentis, Argyope cistellula, and Rhynchonella psittacea) live at this 

 day in the neighbouring coasts* ; and this is in accordance with the 

 opinion of General Portlock, who sees in the records of Tertiary 

 organic life only the evidence of an earlier epoch in the history of 

 the animal world amongst which we live. 



It must, however, be conceded, that at the end of every epoch or 

 section the devastation among its inhabitants was very great, 

 although seldom total. To speak now of the Silurian fossils of New 

 York. Only one escapes upwards out of the Potsdam and Calci- 

 ferous Sandstones, — both being strata of vast extent, in frequent 

 contact or contiguity with others, and often themselves crowded 

 with individuals. The same total destruction occurred in the cor- 

 responding stages of Bohemia. Of the 256 species in Trenton 

 Limestone, 42 survive for a brief space, and then nearly all disap- 

 pear for everf. Of the 22 species in the Medina Sandstone, only 

 two pass upwards; and out of 180 species of every order in the 

 Niagara Section, all die but eleven at the close of the epoch. In 

 Wales the fatality on the occurrence of similar changes of hori- 

 zon, though very considerable, is not so great as in New York : 

 in the Caradoc and Bala beds, as united in ' Siluria,' 2nd edition, 

 78 escape into newer strata, from an assemblage of 328 species; 

 in Wenlock, 88 out of 177 ; but in Ludlow, out of 232, only ten 

 reach some upper stratum, as the Passage Beds, or the Old Eed 

 Sandstone. These examples are all taken from sources of the high- 

 est authority, from the most recent writings of American geologists, 

 as well as from those of Murchison, Portlock, M'Coy, Morris, Sharpe, 

 and others. 



While on the kindred subject of recurrency, a few words on the 

 " colonies " of Barrande may not be amiss. In the centre of the mi- 

 caceous schists (D 4) of the great stage D, in the Lower Silurian 

 Division of Bohemia, lies a very slender and conformable band or 

 wedge of Graptolite-schist, intercalated with trap. It is separated 

 from the next stage upwards, E (Upper Silurian), by 4000 feet of 

 schists and quartzites ; but it contains precisely the same organic 

 remains, and is of the same colour and mineral character. Barrande 

 supposes that the materials of this thin band, with its 61 Upper 

 Silurian fossils, were brought from the N.E., Hke those of the Upper 

 Silurian rocks of Bohemia ; the sediments of the Lower Division, 



^ Bullet. Soc. Geol. France, n. s. vol. xi. p. 177. 



t See " Synoptical View," Table II, Q. J. G. S. vol. xiv. p. 420. 



