256 ANNUAL OF SCIENTIFIC DISCOVERY. 



tion of the fossil species of C is referred to ejections of porphyry and 

 other igneous rocks. 



M. Barrande points out the existence of what he calls colonies of the 

 upper Silurian interpolated in the D group of the lower Silurian. 

 They are beds, sometimes 100 yards thick, having the upper Silurian 

 character in the fossils. M. Prevost observes that if the existence 

 of such colonies can be admitted as proved, (which must require still 

 more investigation,) it indicates a synchronism between two different 

 marine formations, and shows that extended systems of coternpora- 

 neous beds may be paleontologically distinct, while, at the same time, 

 beds of successive ages may be identical in their fossils. Bull. Soc. 

 GcoL de France. 



m .* . 



COMPARISON OF THE STRATA OF THE SILURIAN BASIN OF MIDDLE TEN- 

 NESSEE WITH THOSE OF NEW YORK OF THE SAME AGE. 



THE results of the examinations of Prof. Hall, of New York, and 

 Safford, of Tennessee, were presented by Prof. H., at the Albany 

 meeting of the American Association. 



Prof. Hall commenced by stating that our previous knowledge of 

 this region had been derived mainly from the published reports of 

 Prof. Troost, and from a map of Dr. Owen. From the fossils pub- 

 lished by Dr. Troost, it would appear that the lower and upper Silurian, 

 Devonian, and even carboniferous species occurred together in this 

 basin. Prof. H. said that for several years past Prof. J. M. Safford 

 had been making examinations in this part of the country, the general 

 result of which he had presented in a geological map, showing not only 

 the limits of this Silurian basin, but also the subdivisions which he 

 proposed to make, and which were characterized by certain fossils. 

 The fossils collected amounted to some 200 species, about one half of 

 which were identical with those known in the rocks of New York. In 

 general terms we might say that the rocks of nearly the whole of this 

 basin correspond to the lower Silurian limestones of New York. In the 

 lower portion of the series in this basin, Prof. Safford recognizes three 

 divisions. From the lower of these divisions, he has brought eight 

 species of fossils, and of these eight species five are of species charac- 

 teristic of the birds-eye and Black River limestone in New York, and 

 the other three appeared to be new or undescribed species. From the 

 second division, fifty-eight species had been collected, of which twenty- 

 eight were identical with species known in New York, and mainly 

 those characteristic of the Trenton limestone, a few species only being 

 those which occur in the birds-eye and Black River limestones. In 

 the upper of these subdivisions sixteen species had been found, of 

 which eleven were known as characteristic of New York strata, and 

 nearly all of the Trenton limestone. Prof. Hall had collected a cepha- 

 lopoda of peculiar structure, in the Black River limestone of New York, 

 and had traced its occurrence in the same geological position as far as 

 the Mississippi River, and it occurred also in the basin of Tennessee. 

 In all the localities it was associated with fossils which were in the 

 same geological position in New York. It seemed, therefore, scarcely 



