GEOLOGY. 255 



Silurian to the crowning member of the Tertiary. It was evident that 

 these strata were everywhere plicated and folded, and that the observer 

 passed over a repetition of beds, instead of a succession of beds ; but 

 that the strata, throughout the whole region, had been so shattered 

 by earthquakes, and so metamorphosed by direct or transmitted heat, 

 that it was impossible to identify them, except over limited areas. 



Prof. Agassiz remarked, that he had, at the Cambridge meeting of 

 the Association, urged the importance of a close examination of the 

 older rocks of the Palaeozoic series, with a view of arriving at a stand- 

 ard for determining the order of succession of the contained fossils. 

 It had long been an unsettled question with European geologists, 

 whether we could accurately fix upon the exact point, in the palseozoic 

 rocks, in which animal life had commenced. Mr. Lyell was of opinion 

 that we could not. Yet it is now established, by the labors of Messrs. 

 Foster and Whitney, that we can accurately determine this point, and 

 feel certain that we have ascertained the exact strata which contained 

 the fossil remains of the first created animals. If the zoologist would 

 view with interest the skull of the first created man, it is with equal 

 interest that we see, in the Potsdam sandstones, the evidences of the 

 first created animals. 



ON THE SILURIAN SYSTEM OF CENTRAL BOHEMIA. 



M. BARRANDE, in his observations on the Silurian System of Central 

 Bohemia, recognizes an upper and a lower Silurian, corresponding to 

 what has been made out, first in England, and since in Russia and 

 America. Each of these divisions contains four subdivisions or groups, 

 which he letters A, B, C, D, and E, F, G, H. The lower Silurian con- 

 sists almost wholly of siliceous and argillaceous rocks, to the nearly 

 total exclusion of limestones ; the upper consists mainly of limestones. 

 The limit between the two is marked by eruptions of trap of great 

 extent, which alternate with graptolite schists, in which twenty 

 species of graptolites have been detected. Trilobites, analogous to 

 those of the Caradoc sandstones and Llandeilo flags, (corresponding to 

 subdivision D,) abound in the lower division, while in the upper, great 

 numbers of Cephalopods, Gasteropods, Brachiopods, and Acephala 

 occur, families hardly represented in the lower Silurian of Bohemia. 

 The groups A and B are without fossils, or azoic, and have together a 

 thickness of 24 to 26,000 feet. A is composed of semi-crystallized and 

 argillaceous schists, and B to a great extent of conglomerates, alternat- 

 ing with argillaceous schists ; they pass almost insensibly into one 

 another. C consists mainly of greenish argillaceous schists, and is not 

 over 1300 feet thick. Its fossils are mostly trilobites, and they are 

 peculiar in having the thorax very much developed, with the pygidium 

 very small. The group D, called also the guarlzite division, abounds 

 in siliceous as well as argillaceous rocks, and is very rich in trilobites. 

 Its vertical extent is 8 to 10,000 feet. The several subdivisions from 

 C upward are each distinct in their fossils. Not a species of C occurs 

 in D, and even the genera of trilobites are most distinct. The extinc- 



