168 
HELDERBERG DIVISION. 
the eastern border of Madison county. It is twenty or twenty-five feet thick in Cherry- 
valley. Where the streams from the south in the Heidelberg range open into the valley 
of the Mohawk, this rock is usually exposed on the east and west sides, as at Schoharie 
and Coblcskill creeks. 
Soil derived from this limestone. So far as the disintegrating mass is concerned, the soil 
is of an excellent quality ; but the rock is too limited to exert important effects by itself. 
Thickness. Its maximum thickness is at the base of the Heidelberg, where it is seventy 
or eighty feet thick : at Schoharie, it is sixty feet thick. It is sixty or seventy feet at Be- 
craft’s mountain ; thence, from the Helderberg, or near New-Scotland, it continually 
diminishes in thickness to the west.. 
§ 4. Encrinal limestone (PI. xx. Sec. 5, 6). 
This rock may be considered by itself, or it may be regarded as the terminal portion of 
the preceding rock. It differs from the preceding very clearly in its high crystalline 
structure and light grey color ; but a green matter, or a thin stratum of that peculiar shale 
derived from the same sources as that of the delthyris rock, appears between its layers, 
showing that both rocks were derived from one common origin. In composition, it is 
essentially a pure carbonate of lime crystallized throughout: it is remarkable for the stems 
of encrinites, which, from something peculiar to these organic bodies, give the rock fre¬ 
quently a reddish tint. 
Value as a marble. It is proper to place this mass among the marbles, as it receives a 
good polish, and is used to some extent for mantle pieces and jambs. It is not, however, a 
profitable rock for this purpose. It is a strong durable stone, less subject to decomposition 
than the delthyris shale. 
Thickness. Its maximum thickness is twenty-five feet. It is scarcely ten feet thick at 
New-Scotland. 
Extent. It accompanies the Delthyris shale as far west as Sharon springs, where it dis¬ 
appears ; at least the writer did not observe it at Cherryvalley, where the Delthyris shale 
is not less than twenty feet thick, and where it ought, if continued, to appear superimposed 
upon the shale. Its agricultural characters are unimportant. Its geological relations are 
also scarcely deserving of notice. Above it is the Oriskany sandstone, when that is present. 
The pelvis of a large encrinite, of a mammillary shape, or rather shield-form, and nearly 
two inches in diameter, is considered as its most characteristic fossil. For other relations, 
see PI. XX. sections 1, 2 and 5. 
§5. Oriskany sandstone (PL xx. Sec. 1). 
Among the many interesting rocks of New-York, this, which is placed at the head of 
the section, is one that has always excited its full share of attention. It is not because 
it is economically important, or of great thickness, but rather on account of the number 
