62 PORTAGE GROUP. 



and are less productive than the deeper ones. Below the gravel thin limestones, 

 shales, and clays occur for a distance of about 230 feet before the Upper Helderberg 

 limestones are reached. One of these wells, when sunk to a depth of 200 feet 

 below the surface, yielded, when first opened, 2,000 barrels of oil in twenty-four 

 hours. In some of the wells bored in this vicinity, both oil and water flowed to 

 the surface, and in some of the deeper ones the water is saline. Wells bored into 

 the Upper Helderberg limestone sometimes reached small quantities of oil, but no 

 valuable wells have thus far been discovered in Canada by boring below the 

 Hamilton Group. The flowing wells soon become intermittent, and within a year 

 cease to flow altogether ; they continue, however, to furnish oil by pumping for a 

 limited period, and then appear to be exhausted. The petroleum differs in 

 volatility; the less volatile contains paraffine in solution, and is suited for lubricatiug 

 machinery, while the more volatile is best suited for light. The alliaceous odor of 

 some of the unrefined oil is due to the presence of a little sulphureted hydrogen. 

 Petroleum is modified on exposure to the air by volatilization and oxidation, and 

 eventually assumes a solid form. Thus near Oil Creek, in Enniskillen, the thickened 

 oil formed two layers, called gum-beds, of a viscid, tarry consistence, covering two 

 or three acres with a thickness from a few inches to two feet. In sinking a well, a. 

 bed of this asphaltum, from 2 to 4 inches thick, was met with at a depth of 10 feet, 

 upon a layer of gravel. It contained the remains of leaves and insects, which were 

 imbedded in it during its slow accumulation and solidification. In boring the oil- 

 wells there is always a greater or less disengagement of inflammable carbureted 

 hydrogen-gas, and sometimes it is liberated with explosive violence. The strata 

 almost everywhere in that region hold in a condensed state portions of light carbu- 

 reted hydrogen, which is discharged wherever a natural fissure or an artificial boring 

 furnishes a vent. The shale, on Sulphur Island, at the mouth of Thunder Bay in 

 Lake Huron, is so highly charged with bituminous matter that it has been set on fire 

 and burned for months. The bitumen burns out and leaves the shale with a reddened 

 appearance. 



CHAPTER XXII. 



PORTAGE GROUP. , 



130. This Group was named from Portage, New York, and defined by Hall 

 in 1843. It consists of variable shales and sandstones, forming in New York an 

 east and west band, resting upon the Hamilton Group, aud dipping south about 25 

 feet in a mile. The sandstones produce falls in the streams, beautiful cascades, 

 and grand and striking^scenery. The highest perpendicular fall of water and deepest 

 canons and 'gorges in the State exist in this Group. It thickens westerly and 

 thins easterly, and does not extend to the extreme eastern part of the State. 

 Sandstones greatly predominate in the eastern part, while shales increase westerly, 

 until the whole Group becomes a mass of black, bituminous shale. The thickness 

 on the Genesee is 1,000 feet, on Lake Erie 1,400 feet. A considerable part of 

 Lake Erie is excavated out of this Group, which shows a belt on the south side ex- 

 tending nearly to Sandusky ; and from here it bends southerly across Ohio, leaving 

 Columbus to the west, and, reaching the Ohio River below the mouth of the Scioto, 



