164 GEOLOGY OF THE TfflRD DISTRICT. 



mass at innumerable points. The usual tliickness is about fourteen feet ; the greatest ob- 

 served thickness, twenty feet. 



It has not been seen beyond the town of Smyrna in an east direction ; but from thence 

 west it extends into the fourth district, through Madison, Onondaga and Cayuga. Its locali- 

 ties are numerous in the last two counties ; but it was not seen in Madison, though it must 

 exist there. The Tully limestone makes a good, but not a white lime ; owing, in all proba- 

 bility, to the presence of carbonates of iron and manganese. These two minerals, as high up 

 as tlie coal deposit, appear to increase from the Hamilton group, as the age of the rock di- 

 minishes. Minute veins of carbonate of iron are seen in the limestone ; and the fossils of 

 the rocks above it are often replaced by the two carbonates, particularly the encrinital stems 

 and disks. 



There are two fossils in this rock which are wholly peculiar to it. The first is the Cuboidal 

 atrypa, No. 1 of the wood-cut. This is an English name, given to a fossil by Mr. Phillips, 

 which, from the figiire and description conjoined, shows identity with that of the Tully lime- 

 stone. It is placed in the Devonian system, which gives but a feeble light as to the geologi- 

 cal identity of the strata in which they are found. The precise position which the cuboides 

 holds in New- York, will soon determine the position of its kindred one in England. The 

 cuboides is found in most of the localities of this rock. 



No. 2. The T\illy orthis is the other fossil : It appears also to be an English one, from 

 Mr. Conrad's information, having been described years ago by Martin, under the name of 

 Anotnia resupinata ; but the former name is preferred, being a sure one. 



No. 3. The Lentiform atrypa (A. lentiformis), from its shape like a lentil or lens, has 

 always been considered by Mr. Conrad as the young of the A. prisca. It may be so ; but 

 its size is remarkably uniform, both in this rock, and in the corniferous and others. Its 

 numbers are great, and show no intermediate sizes, and none of the larger kind are found in 

 the Tully limestone ; all which facts indicate a shell that had attained its growth, rather than 

 a growing one. It is figured in order to draw attention to it, and from its constant association 

 with Nos. 1 and 2. 



There are other fossils in this rock, but they are rare, with the exception of a very small 

 orthis at Smith's ledge, and a Slrophomena resembling the linear, which occurs in great abund- 

 ance in the upper part of the limestone at Tully four-corners. Among the others, are the 

 Calymene marginalis, the Avicula reticulata, and the Atr)'pa didyma. Both of the latter are 

 also European fossils, which I have not yet seen. By their means, Mr. Conrad beUeves that 

 he has shown the identity of the Tully limestone with the Aymestry limestone of Mr. Mur- 

 chison. 



Localities where observed. The first point going west, is on the turnpike from Sherburne 

 to De Ruyter, about eight miles from the former village. It appears in a low side-hill, forming 

 the bank of the creek where the road crosses it. About four layers are exposed, ranging by 

 the side of the creek. It is more impure there than farther west. 



In Madison county it was not seen, but it must exist there, as it is found to the northwest 

 of Dc Ruyter village, about two miles distant. It appears in tlie hill-side more than one 



