60 HAMILTON GROUP. 



most characteristic species among the invertebrates, and those by which the rocks 

 may be readily identified are Cyatliophyllum rugosum, Favorites goldfwm, Syringopora 

 maclurii, Phillipsastrea vemeuUi, NucUocrinus verneuili, Spirifera acuminata, S. 

 gregaria, Pentamerus knighti, P. aratus, StricHandinia elongata, Paracyclas occident- 

 ali8, Conocardium subtrigonale, Platyceras dumosum, Tentaculites scalariformu, :in<l 

 Dalmanites selenurus. In the vicinity of Davenport, Iowa, it furnishes an 

 abundance of durable and massive building material and contains cavernous 

 openings, as if worn out by the action of water, and filled up subsequently with 

 material derived from higher rocks, and especially those of the Hamilton Group. 

 The quarries at Columbus, Ohio, and North Vernon, Indiana, are in this Group. 

 The strata in the vicinity of the Straits of Mackinac have been eroded and 

 excavated so as to produce the Island of Mackinac, and large masses of the 

 materials have been transported and distributed over Southern Michigan and Ohio. 

 £ 125. The limestones of this Group in Canada are usually bituminous, aud 

 petroleum frequently fills the cells of corals aud other fossils. The corals often 

 prevail in distinct bands, some of which will be saturated with the oil, while others 

 will not. Petroleum springs rise from this Group at Tilsonburg, and other places 

 along an anticlinal which runs through the Western Peninsula. The oil being 

 lighter than water, and permeating the strata, naturally rises to the highest part of 

 the anticlinal between the impervious layers of rock, and escapes to the surface. 

 In other localities the bitumen is solid, and takes the form of asphaltum or 

 mineral pitch, as at Kincardine, where slaty beds contain from 10 to 15 per cent 

 of bitumen soluble in benzole. No good well, however, has been discovered in 

 Canada by boring in these rocks, though it has been contended the oil at 

 Enniskillen and on the Thames has its source here. Where the oil has been found 

 in this Group, it has had its source in the Waterlirae or in the shales below. 



CHAPTER XXI. 



HAMILTON GROUP. 



^ 126. This Group was named from Hamilton, Madison County, New York, 

 and defined by Vauuxem in 1842, though he did not include within it the 

 Marcellus Shale, Tully Limestone, and Genesee Slate. The divisions made for it 

 in New York are Marcellus Shale, Ludlowville Shale, Encrinal Limestone, Moscow 

 Shale, Tully Limestone, and Genesee Slate. The rocks are not susceptible of this 

 divisiou, except locally, and they all belong to a single Group. The Marcellus 

 Shale was named from Marcellus, where it is an argillaceous slaty rock, bearing 

 much carbonaceous matter, and sometimes small pieces of coal, and has a thickness 

 of about 200 feet. It contains layers of impure limestone, and abounds in fossils. 

 In many places it contains so much bitumen as to give out flame when thrown 

 into the fire, which led the early settlers to explore it throughout its whole extent 

 for coal, only, of course, to suffer disappointment. It is not separable from the 

 Ludlowville Shale by any well-defined characters. The Ludlowville Shales were 

 named from the town of that name, and separated from the Moscow Shale by a 

 layer of limestone 3 or 4 feet thick, called the Encrinal limestone ; but such 



