No. 136.] 51 



In Canada West, near Gait, there is a limestone believed to 

 belong to this group, but which seems not to have been formed 

 in New-York, which contains some remarkable fossils, especially 

 some large bivalve shells named by Prof. Hall, Megalomus, 

 specimens of which are in the cases. 



The Onondaga-salt group is hardly seen east of Herkimer 

 county, though in Pennsylvania it seems to re-appear, but without 

 saline springs. Westward it extends to Iowa, but there contains 

 no useful minerals and few fossils. 



Above the Salt group succeeds a thick series of strata, chiefly 

 limestone, but with one or two sandstones among them, known 

 under the general name of the Helderberg rocks, as they form 

 the great escarpment of the Helderberg hills in Albany county. 

 From this place their edges may be followed in the hills lying 

 back from the Hudson, along the base of the Catskill mountains, 

 and through Ulster county as far as Kingston and Rondout; 

 whence they bend southward and extend along the hills west of 

 the valley of the Delaware and Hudson Canal, passing out of the 

 State near the northwest corner of New-Jersey. They run still 

 farther southeastward, are seen above the Delaware water-gap ; 

 and their lower strata are traceable in the Appalachians as far 

 as Tennessee, though their upper limestones do not extend 

 beyond the Susquehanna. In following them westward, we find 

 their lower limestones and sandstones thin out rapidly, not 

 extending beyond the Niagara in any considerable thickness, 

 while their upper limestones are found spreading into the far 

 west. 



This series of rocks may be divided into four portions ; the 

 Waterlime group, the Lower Helderberg limestones, the Hel- 

 derberg SANDSTONES, and the Upper Helderberg limestones. 

 Lowest lies. 



THE WATERLIME GROUP 



of Central New- York, a succession of dark-colored, usually fine- 

 grained and straight-bedded limestones, attaining in Madison 

 county the thickness of over 100 feet. They lie immediately 

 over the grey and drab limestones of the upper part of the Salt 

 group, and are not divided from them by any very distinct or 

 sudden change in the appearance of the strata. Their name is 

 given from the water-lime or hydraulic cement which is exten- 

 sively manufactured from two of the layers toward their upper 

 [Assembly, No. 136.] S 



