BIGSBY PALAEOZOIC ROCKS OF NEW YORK. 347 



stone, with thin courses of limestone and limestone-breccia, the 

 upper portions in many places abounding in fossils. The shales are 

 dark-blue, brown, and black ; the gritty sandstones and grits are 

 grey, greenish, and bluish-grey. This rock is so diversified as to 

 have merited the name of "Protean," its mineral characters 

 changing essentially at distant localities. 



On the River Hudson, and in many other parts of New York, 

 this rock is a slate with thinly-bedded sandstones, formerly called 

 "argillite" and ° greywacke " (Hall). It is often altered in cha- 

 racter, deranged in position, and apparently mixed with more 

 ancient schistose rocks (Vanuxem, p. 60). A green or olive colour 

 is very characteristic of this group (Vanuxem). It is often sub- 

 divided into the three following portions : — 



1. (From below.) Frankfort slate and sandstone. 



2. Green slates. 



3. Pulaski sandstones or Loraine shales (Emmons, Rep. p. 119). 

 The first and third portions have received their names from the rock 

 being well characterized at the localities mentioned. 



It is a most remarkable fact that the Frankfort Slates give out 

 brine-springs, as at Saltspringville and at Balston. These are the 

 lowest saline springs known. 



Transition. — Sometimes this group is distinct from Utica Slate ; 

 but in general there is no mineral line of division between them, the 

 change being gradual. 



Place. — This is another of the constant groups, and is met with 

 in middle North America wherever there is a sufficiently deep 

 rupture among the sedimentary strata. It occupies much of the 

 middle and eastern parts of New York (valleys of the Hudson, Mo- 

 hawk, &c.) in broad masses which spread northwards into Canada, 

 and southwards into New Jersey and Pennsylvania, but often in 

 bands attenuated by the accidents of the ground. Westward it 

 crosses from the State of New York, over Lake Ontario, and over- 

 spreads much of Upper Canada on its way to the south side of Lake 

 Superior, where it follows the southerly course of the other Silurian 

 groups. The exact outlines of this group have not yet been traced 

 in New York, from the wild and intricate nature of the region it 

 often occupies. It is in great force in Albany, Schenectady, Scho- 

 harie, and Saratoga Counties, and may be followed from Saratoga 

 Lake into New Jersey and beyond (Mather, p. 375). One line 

 of east and west outcrop is 1220 miles long — that from the Mas- 

 sachusetts frontier to the south border of Wisconsin near Jonesville, 

 — while its extension from Gaspe of Lower Canada, down the 

 valley of the Hudson, &c, to near Harrisburg, is 1400 miles 



lon s- 



This group is seen largely in Ohio, Kentucky, Indiana, Missouri, 

 and on the River Mississipi, beyond Dubuque. 



Position. — In the vicinity of intrusive or metamorphic rocks, the 

 dip is high, and in various directions ; but at some distance from 

 these it is small, and very small generally toward the west and 

 south. The dip in Orange County, New York, is 50°, and south- 



VOL. XIV. PART I. 2 A 



