ESTHERIA OVATA. 91 



at Greenfield, Conn.), Ave may observe a nearly general coincidence in the occurrence of 

 Upper and Lower Conglomerates, wliicli may possibly be a guide in correlating tlie 

 deposits of the several areas. As little, hovrever, has been determined strictly as to this 

 correlation as has been fixed with regard to the exact geological age of this great group 

 of strata.^ Prof. E. Emmons has sketched out the members of the Deep River series 

 (estimated at upwards of 6000 feet in thickness) ; he indicates two chief horizons, far 

 apart, at which Saurian remains, Plants, Estheria, and other fossils, occur ; and he believes 

 that the distinctions of the fossils are so great, the amount of accumulated deposit so vast, 

 and the evidence of unconformability so important, that he has reason to refer the lower 

 portion of the series (Chatham group) to the Upper Palaeozoic (Permian), and the upper 

 portion to the Lower Mesozoic (Triassic) age respectively. 



This conclusion seems to me invalid, and the palaeozoic evidences are very poor 

 indeed ; but it does not concern us at present, the Estheria alone demanding special 

 attention ; and of these I have seen specimens only from Dan River, from Richmond, 

 and from Pennsylvania, none from the Deep River series. Prof. Emmons figm-es a 

 specimen from the Chatham series [Posidonia ovalis), and two forms from Dan River 

 {P. multicostata and P. trigonalis). If the conglomerates in the several basins should be 

 indicative of certain correlative horizons (as above referred to), all these Estheria would 

 apparently belong to the same (lower) group ; and the Estheria of Richmond, Va., would 

 seem to belong to the same horizon. Prof. Emmons, however, refers the Richmond coal- 

 field to the age of the upper part of the Deep River series (if I understand him aright). 



I have not been able to discern any essential difference between the Estherics from 

 Pennsylvania, Virginia, and Dan River (North Carolina) ; and they might therefore well 

 belong to the same horizon, whatever those from the Deep River series may turn out to 

 be. Of the latter we have figures, given by Prof. Emmons, which help us, however, 

 little or nothing in specific determination, for I am quite prepared to say that ordinary 

 artists and amateur draughtsmen would make as many and as variable sketches of one 

 and the same Estheria, in different states of preservation, as the three given us of 

 P. multicostata, P. annularis, and P. ovalis, and we will include also the far better wood- 

 cut of the Richmond Estheria given by Lyell. The last mentioned is equivalent to our 

 fig. 28 ! Fig. 28 represents the same species as do figs. 26 and 27. And specimens of 



^ If the reader will consult Prof. H. D. Rogers's ' Essay on the Geology of the United States,' in the 

 last edition of A. Keith Johnston's ' Physical Atlas,' he will there find the stratigraphical conditions of the 

 Mesozoic sandstones and shales under notice amply and, I believe, correctly treated. Whatever maybe the 

 thickness of the several strata, measured perpendicularly and added together, — a thickness far surpassing, in 

 Connecticut, according to Prof. Hitchcock, that of either the Triassic or the Jurassic strata of Europe (' Ele- 

 mentary Geology,' new edition, 1860, p. 409), yet, as these deposits have been formed in confined areas, and 

 on sloping shores, it appears to me that Prof. Rogers' observations must satisfy any dynamic geologist that 

 no great vertical displacement of the area has been required for the accumulation of this sedimentary mass 

 in the shallow waters of the old sub-Appalachian water-belts. 



