TRENTON GROUP. 43 



sufficient to cover a thin shell. There is no evidence of any difference between the 

 temperature of the water then and now, nor between the climate then and now. 



§ 85. Wherever the Black River limestone exists, the Trenton is conformable 

 with it ; and where the Black River is not distinguished, the Trenton is usually con- 

 formable with the Chazy. The Trenton is conformable with the Utica Slate above, 

 in New York and Canada ; but there is an abrupt change in the character of the 

 rocks, and a marked difference in the fauna, while in Kentucky it graduates 

 up into calcareous shales of the age of the Utica Slate by imperceptible grades, so 

 the line of separation can not be determined, except as based upon a slowly 

 changing fauna. 



§ 86. Light carbureted hydrogen gas is often the product of the transforma- 

 tion of organic matter at ordinary temperatures, and is abundant in the palaeozoic 

 rocks from the Chazy to the Permian. A spring at Caledonia, Canada, issuing 

 from the Trenton Group, evolves 300 cubic inches of carbureted hydrogen gas 

 per minute. It is saline water. Another discharges somewhat less, and another 

 discharges large quantities of sulphureted hydrogen gas. This is not considered 

 surprising when it is remembered the Chazy Group in the Ottawa Valley includes 

 a considerable thickness of shales and argillaceous limestones, and the Quebec Group 

 offers successions of limestones and shales, whose slow decomposition from infil- 

 trating waters will furnish such gases. In higher strata, however, the carbureted 

 hydrogen gas escapes in much greater quantities, as at the burning spring near 

 Niagara Falls, and in the region of the oil-wells. Carbureted hydrogen gas is the 

 well-known "fire-damp "of the coal-mines. It collects in ill- ventilated galleries of 

 collieries, and when sufficiently mixed with the atmosphere, if it comes in contact 

 with an unprotected flame, it explodes with great violence. It exudes from all 

 rocks charged with petroleum or naphtha, and was known and used for fuel before 

 the Christian era on the Caspian Sea, where it is evidently inexhaustible. Petroleum 

 occurs in the cavities of fossils, Orihoceras sometimes holding serveral ounces of it, 

 at Pakenham and Lancaster, Canada. While both carbureted hydrogen and 

 petroleum occur in the rocks of the Quebec and all succeeding Groups, yet none 

 has been found of commercial value as low as the Trenton. The reasons are, 

 absence of porous strata and cavities for its collection, and because the animal 

 and vegetable matter was not collected in sufficient quantity at any single locality. 

 It has been asserted the gas in Western Ohio and Northern Indiana is from this 

 Group, but the author thinks all the evidence is against such conclusion. 



