160 T. Sterry Hunt on the Chemical and Geological History 
matter. Pyroschists are well known to occur in almost every 
gecboion! group from the Lower Silurian to the — ~ 
are often, lke coal, employed as valuable sources of vo 
hydrocarbons, although like it they contain little or no vice 
‘They may be regarded as clays or marls, holding, in a state of in- 
timate admixture, a variable proportion ‘of a matter approaching 
to coal in its chemical characters. Although frequently dark 
brown or black in colony they are simetiines ‘ight brown or even 
yellowish-gray, as is the ease with the Jurassic pyroschists of 
the department of the Doub, and those of the Tertiary wate! 
near Clermont, both in France. Remarkable examples 0 
this are also given by Prof. J. D. Whitney in the pyroschists 
from the Utica formation of the Lower Silurian series in Iowa, 
which were yellowish-brown, weathering to a bluish-ash color. 
They however blackened when exposed to heat, burning with @ 
bright flame, and contained from eleven to twenty per cent of 
combustible matter. The black, — and apparently very 
carbonaceous shales from the valle ey of the Hudson River, 
were found by Dr. Chandler to éontain from one-half to one per 
ters.* (Geology of Iowa, i, p. 859.) A pyroschist of the Utica 
formation, from Collingwood on Lake Huron, examined by my- 
“In the Report on the Geological Survey of Iowa, (vol. i, p. 183) Prof. bi | 
has given the results of a series of careful analyses of pyroschists of the 
River group, (in which he includes the Utica formatio nalyses em 
imens from the lead region of Wisconsin, from lala Hur ne Ottawa, and 
e district of Quebec. They were made by "Messrs. Chandler God Kimball, who 
Seer i : A 
the organic elements in the residue. e specimens, like those noticed abov 
the mineral matter was almost sis iiteasent others, like that ye Collingwood 
were highly calcareous, and some contained a consi iderable proportion of carbona 
o ia. We select, from the eight analyses given, five of the more oer 
istic examples, 
I, A dark shrogelatas2 itiote -gray-weathering siliceous shale, from the lead re 
ion, without traces o| nic remains. When heated ina close vessel it gave off 
412 per vara “es eat combustible matter, leaving 6°84 of carbon, which was 
remov ae by ca 
dark gra sey sihaled with a few graptolitic markings, from the same region. 
tl, a A dark brown, ae fiue grained, eens laminated rock, without fossils, from the 
islands north of Maple Cape, Lake 
' IV. A black bituminous shale, fitted ‘with crinoids and trilobites, from Gloucester, 
~ Otta’ seg 
A poe wn rock, mile Gutter laminated, and showing traces of graptolites, 
ad: the Ste. pa, boy be 
a ae 
a Il. Ill. IV. Vie 39 
y and — 13°57 8065 34,60 48 27 37:26 | 
Carbon, 15°03 3:97 663 699 “61 
ye 1°65 2 63 aT 118 83 
5:39 4°87 2-96 3°39 171 
Carb. lime, 29 477 493 20°30 eee 
Carb, magnesia, 46 3:40 2:53 1148 2. 
Alumina and iron oxyd, 2-79 1:99 2-09 1% 329 | 
; 100°48 10028 98:89 99°55 99.72 
