PORTAGE GROUP. 63 



it crosses into Kentucky, and is soon broken up in the spurs of the mountain 

 ranges. It crosses Lake Erie, and occupies a small part of the Canadian penin- 

 sula, and enters the southern peninsula of Michigan, where Winchell called it 

 the Huron Group. From Michigan it crosses the north-western corner of Ohio, 

 and enters Indiana, forming a belt across that State by way of Indianapolis, and, 

 reaching the Ohio River at New Albany, crosses into Kentucky, and extends far 

 toward Tennessee. It was called the Black Shales in the Geological Survey of 

 Ohio for 1838, and in that of Indiana for 1839, and in later surveys of Kentucky, 

 Indiana, and Tennessee. The thickness in Ohio is from 200 to 1,000 feet or more, 

 in Indiana from 100 to 200, and in Tennessee from 10 to 150 feet. It has never 

 been recognized west of these States, and is therefore classed as a Group belonging 

 to the Appalachian mountain system. 



131. Fucoids, wave-lines, and ripple-marks are numerous, and occur 

 throughout its distribution. The paucity of fossils in this Group, when compared 

 with those above and below it, is one of its striking characters. Whole days may 

 be spent in some parts of it without finding a shell, though fucoids are in the 

 greatest abundance. Land-plants occur in profusion in New Brunswick, some of 

 which are of gigantic size. Goniatites complanatus, Panenka spedosa, and Spirifera 

 Icevis occur in New York and in Ohio, and may therefore be considered character- 

 istic. Fish of large size, covered with thick heavy plates, and having jaws and 

 teeth strong enough to crush a body the size of a man, occur in it. Cladodm, 

 a carnivorous fish, became abundant in this period, and flourished until the Per- 

 mian. It was world-wide in its distribution, and its vertical range exceeds that 

 of any other genus of fishes. The Group seems to have been deposited in internal 

 seas or arms of the ocean, and is the last Group of the Devonian System, having a 

 large geographical distribution, for the Chemung and Catskill are comparatively 

 local in their extension. In Ohio there are large concretionary balls of impure 

 limestone, some of them several feet in diameter, and it was in one of these the 

 monster Dinwhthys was discovered. 



132. The Group is distinguished as the great seat of petroleum, and is sup- 

 posed to be the source from which the chief supply in this country is derived. In 

 New York, Pennsylvania, and Ohio the wells are bored through the overlying 

 rocks until the Portage is reached, or the saturated sands that overlie it furnish the 

 supply. Ten per cent of the shales is bituminous and carbonaceous matter. The 

 shale yields oil by distillation, and gas and oil springs abound in its sandstones, 

 and in those which overlie it. The great oil-sands in the oil regions of Pennsyl- 

 vania belong to the Chemung, and have doubtless been fed as well from the shales 

 of this Group as from those of the Chemung, which furnish the same products. 

 The gas at Fredonia, New York, in this Group, was used for lighting houses in 

 1820. Lyell described it in his travels in 1841, and it has been in constant use, 

 with little variation in the supply, ever since. 



