TKENTON LIMESTONE. 67 



I have devoted a considerable space to the illustration of this species, and my only 

 apology must lie, tliat since the work will he mainly dislriliulod among learners, I desire 

 to make it readily understood by them. If therefore the author's own labors can in any 

 manner be offered as a substitute, the student may find his task easier than to be left in 

 such cases with a single illustration, while many hours of labor might be refjuired to 

 convince himself that all these forms were identical. 



Position and locality. This species occurs in infinite numbers in the Trenton limestone, 

 and in nearly every part of the rock. In some localities the hemispheric, and in others the 

 cylindrical and ramose forms prevail, and not unfrequently both occur together. 



This species commences its existence soon after the final deposition of the Calciferous 

 sandstone, where it is somewhat rare. In the Trenton limestone it presents its maximum 

 development, but is still quite common in the Hudson-river group. At the west it is equally 

 abundant and protean in its forms in both these groups, acquiring its maximum development 

 at a higher point, geologically, than in New-York. The same species apparently reappears 

 after the deposition of the Oneida conglomerate, and is found in the Niagara group, as 

 well as in the Pentamerus and subsequent limestones. A similar, if not identical species, 

 occurs in the Hamilton and Chemung groups. 



Its geographical range is equally extensive with its geological range. It occurs in nearly 

 every part of New-York, in many places in Pennsylvania, in Virginia, Kentucky, Ten- 

 nessee, Ohio, Indiana, Michigan and Wisconsin, as well as Canada. 



Its priiicipal localities in the Trenton limestone, are Trenton Falls, Middleville, Jackson- 

 burgh, Walertown, Lowville, Turin, Plattsburgh, Chazy, Glen's Falls, and numerous 

 other localities in the Mohawk, Champlain and Black River valleys. (State Collection.) 



102. 3. CmETETESI RUGOSUS («. s;j.). 



Pl. XXIV. Figs. 2 a, b. 



A polymorphous or ramose coral ; branches somewhat compressed ; tubes radiating 

 almost vertically from a central axis ; diaphragms numerous, regular ; interior walls of the 

 tubes rugose, or transversely wrinkled. 



The tubes are larger, the interior distinctly rugose, and otherwise presenting a somewhat 

 different aspect from the preceding, to which, however, it is closely allied. The specimen 

 figured shows a ramose form, the branches diverging in three directions, but they have 

 been broken off before the coral was imbedded. 



Fig. 2 a. The specimen of the natural size. 



Fig. 2 b. An enlarged portion, showing the form of the tubes and the rugose interior. 



Position and locality. In the lower part of the Trenton limestone, at Middleville, Herki- 

 mer county. 



9* 



