ISS PARALLELISM OF THE LOWER SILURIAN GROUPS OF TENNESSEE AND NEW YOR1C [1854 



retreatings of the cells, here and there, but which soon become The Treuton species thus appear to lose their value in Middle 

 prominent from furrows, and at last the whole form stands boldly Tennessee, as cliaracte: istic of a subdivision of the Lower Silurian 

 out. rocks. * 



It is very different, however, with the species of the other 

 New York groups. The Stones River group has throughput 

 (excluding the Trenton species) a well marked Black River 

 fauna ; and so the Nashville group, which succeeds it, has a 

 decided Hudson River fauna, while at the same time there is no 

 blending of these characteristic species. 



To illustrate these remarks, I have constructed the table on 

 the following page, using all the described species common to 

 the two States, excepting those found, either in both the Tennes- 

 see groups, or, in both the Black River and Hudson River 

 groups of New York, for these do not bear upon the points 

 before us; this excludes such species as Orthis iestudinia, 

 Pleurotomasia wmbilicata, Leptana scricea, L. atlernata, Chcc- 

 tetes columnaris, Murchisonia bicincta, &c, &c. Several 

 doubtful species have also been excluded. 



This table illustrates the blending in Tennessee, of Trenton 

 with Black River species below, and Hudson River species above ; 

 and, also, the fact, that the characteristic Black River species are 

 confined to the Stones River Group, while those characteristic of 

 the Hudson River rock, are confined to the Nashville Group. 



After proceeding with this subject in an able manner and to 

 some considerable length, the learned author says: 



If, in this discussion of some of the highest relations of phy- 

 siology, we have not wandered too far from our subject proper, 

 which we have thereby sought to illustrate, indirectly, we will 

 revert to the thread of its discourse for a few concluding 

 remarks : 



The final question now is, what is the legitimate interpreta- 

 tion of these reproductive phenomena of the Aphides we have 

 described 1 My answer to this has been anticipated in the fore- 

 going remarks. I regard it as nothing but a rather anomalous 

 form of gemmiparity. As already shown, the viviparous aphides 

 are sexless ; they are not females, for they have no proper female 

 organs, no ovaries and oviducts. These viviparous individuals, 

 therefore, are simply gemmiparous, and the building is internal 

 instead of external, as with the Polyps and Acalephs ; it,moreover, 

 takes on some of the morphological peculiarities of oviparity, but 

 all these similar conditions are economized and extrinsic, and do 

 not touch the intrinsic nature of the processes concerned therein." 

 — Proceedings of the American Association — Annals of Science 



On the parallelism of the lowjr S r lurian groups of Middle 

 Tennessee with those of New York.* 



BY PKOF. J. M. SAFFOBD. 



The Lower Silurian rocks of Middle Tennessee are divided 

 into two natural, and well characterized groups. The Lower 

 division, which has been named the Stones River Group, is a 

 series of bluish and dove-colored limestones from 250 to 300 

 feet thick. These rocks are the lowest visible in this part of the 

 State. 



The Upper division, named the Nashville Group, is, in great 

 part, dark bluish limestone, about 400 feet in thickness. We 

 are acquainted with 200 species from these rocks, of which one 

 half are new, the others being identical with New York species. 



The Tennessee strata, under consideration, are the equivalents, 

 generally, of the following New York groups: first, the Black 

 River group (including the Chazy, Birdseye and Black River 

 limestones) ; secondly, the Trenton limestone ; and thirdly, the 

 Hudson River group (including the Utica slate.) 



This general parallelism is very clear and satisfactory. When 

 we come, however, to search, in Temiessee, for the Trenton lime- 

 Btone, separated, as a distinct group, from the Black River rocks 

 below, and from the Hudson River above, we are entirely lost. 



The difficulties are these : First, many of the species, belong ■ 

 ing exclusively to the Trenton limestone in New York, occur, in 

 Middle Tennessee, mingled in the same strata with Black River 

 fossils; in fact, many of them occur in a lower position than 

 some of the Black River species, for instance the following 

 group, Stromatocerium rugosum, Streptoplasma profunda, and 

 Columnaria alveolata, is highly characteristic of the uppermost 

 member of the Stones River Group ; notwithstanding this the 

 central part of the same group affords such Trenton fossils as 

 the following : Reteporafenestrala, Subulites elongata, Cyrtolites 

 comprestus, Bucania bidorsata, Bucania expansa, &c, &c. In 

 the second place, if we take the Nashville group, and study its 

 Trenton, and Hudson River fossils, we find the same blending of 

 species, some of the Trenton running up to the very top of the 

 group, and some of the Hudson River appearing at its base. 



• Proceeding-* of the American Association — Annals of Science. 





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-In view of all these facts it follows; First, that the Trenton 

 limestone, as a distinct group, cannot be recognised in Middle 

 Tennessee ; and, Secondly, that the Nashville and Stones River 

 groups are, respectively, the representatives of the Hudson River, 

 and Black River groups of New York, and that the former rests 

 directly upon the latter. 



It may be added too, that the facts, thus developed in Ten- 

 nessee, show that it will hardly be satisfactory to unite, as has 

 been suggested, the Trenton limestone, as a group, with the 

 Hudson River recks, for the blending of species takes place 



