28 THE GEOLOGIST'S TRAVELING HAKD-BOOK. 



7. Lower Helderberg. In consequence of these rocks being so well developed 

 on the Helderberg Mountains, near Albany, New York, they have received that 

 name. The Lower Helderberg series consists of five limestone sub-divisions, and 

 the Upper Helderberg of four members. They are separated by an important 

 sandstone formation the Oriskany. The Lower Helderberg, which is well 

 developed in the eastern part of New York, thins out in going west, and at 

 Syracuse disappears entirely. The sandstones also thin out and disappear, so that 

 at Syracuse the Upper Helderberg rests on the Water-lime, the upper member of 

 the Onondaga Salt group. The Lower Helderberg consists, in ascending order, 

 of the 1. Tentaculite limestone, the 2. Pentamerus limestone, the 3. Delthyris shaly 

 limestone, the 4. Encrinal limestone, and 5. Upper Pentamerus limestone. 



1. The Tentaculite limestone is the lowest member of the series. Portions 

 of it afford fine building stone, which can be procured in blocks of large size, 

 perfectly solid, and free from cracks or flaws. They vary from ash-gray to black, 

 and present almost every shade between these colors. The strata are intersected 

 by two main systems of joints nearly perpendicular to each other, hence the 

 rock can easily be quarried in large blocks. But much of it is thin-bedded, 

 often thinly laminated, dark blue ; its color, texture and composition contrast- 

 ing strongly with the Water-lime below. H. The 2. Pentamerus limestone 

 is rarely pure, being more or less mixed with black shale, which gives a dark 

 color to the rock, it being usually a dark gray. It is crystalline in grain, and is 

 in layers, but the lines of division are not straight, and the surface is not even. 

 The whole mass has a rough appearance, and it does not make a good building 

 stone. V. The 3. Delthyris shaly limestone, as its name implies, is a shaly mass, 

 and consists of alternate beds of shaly and compact limestone. It is an exceedingly 

 interesting rock from the great number of species, the abundance and perfection of 

 its fossils. Hall, 144, The 4. Encrinal is a compact crinoidal limestone, and the 

 5. Upper Pentamerus is a bluish gray limestone. In Pennsylvania, according to 

 Rogers, the Lower Helderberg is 50 to 100 feet thick, a diversified calcareous 

 formation, of some shade of blue, argillaceous and flaggy in its lower beds, and 

 shaly towards the middle, with layers and nodules of chert. 



8. Oriskany Sandstone. In New York the greatest thickness of this rock is 

 not more than thirty feet, and usually much less, but in Pennsylvania, Maryland 

 and Virginia it is, in places, as much as 700 feet ; even hi New York it covers an 

 extensive surface, and is strongly marked in its fossils, which are generally of a 

 large size, and attract the attention of travelers. At the typical locality, Oriskany 

 Falls, the sandstone is twenty feet thick, and is of a light yellow color, friable, and 

 readily crumbling into pure sand ; no part of it being sufficiently solid for durable 

 work. One characteristic of this rock is the abundance of small cavities, which 

 have been formed by the destruction of fossils. These present themselves in all 

 cases where the rock is well developed. The porous nature of the mass has 

 admitted the percolation of water, which has dissolved the calcareous matter of 

 the shells, usually leaving casts of their internal structure. As a mass the 

 Oriskany sandstone is a coarse, rather loosely cemented, purely silicious sandstone, 

 of a yellowish white color. Sometimes it is shaded brown or some other dark color. 

 In Pennsylvania it forms rough ridges, with a poor sandy soil. It is used for glass- 

 making, and contains an iron-ore too silicious to be valuable. Some of our geologists 

 (Hall, Rogers, Dana, etc.) place the Oriskany at the top of the Silurian series. 

 and others (Newberry, Lesley, Hunt, etc.) at the bottom of the Devonian. 



