754 APPENDIX. 



species that have no external shell. The earliest of this kind were probably the 

 Conularise, as already stated. 



Page 597. — In the sub-kingdom of Radiates there are two comprehensive 

 types intermediate between the classes of Polyps (the inferior) and Acalephs 

 (the next higher). (1.) That of the Cyathojrfiylloid corals, whose fundamental 

 structure is based on the number 4, the number eminently characteristic of Aca- 

 lephs, the rays being multiples of four, and not (as in modern corals) of six. 

 (2.) That of the Faoosites family of corals, which, if related to modern Mille- 

 pores and true Acalephs, as Agassiz holds (p. 162), belong to that division of 

 Acalephs which embraces species so polyp-like that until recently they were 

 arranged with Polyps. The species of these comprehensive types are the only 

 known representatives of Polyps and Acalephs in the Palaeozoic faunas, except- 

 ing possibly the Graptolites ; and these, if Acalephs (p. 190), are Hydroids like 

 the Favosites. 



Coral-making Mollusks (Bryozoans), Polyps, and Acalephs, were a prominent 

 part of that harmonious assemblage of groups which constituted the life of the 

 Palaeozoic. 



G. — Mineral Oil. 



Mineral Oil, or Petroleum, is a bituminous liquid resulting from the decom- 

 position of marine or land plants (mainly the latter), and perhajis, also, of some 

 non-nitrogenous animal tissues. It proceeds from rocks of various ages, from 

 the Lower Silurian to the Post-tertiary, and from limestones and sandstones, as 

 well as shales. The so-called anthracite of the Calciferous beds of New York is, 

 according to T. S. Hunt, an altered and inspissated mineral oil ; and liquid drops 

 of the original material sometimes exist in the quartz crystals of the same region. 

 In the Bird's-eye limestone of Riviere a la Rose (Montmorenci), Canada, and of 

 Watertown, N.Y., it flows in drops from a fossil coral; and in the Trenton lime- 

 stone at Pakenham, Canada, it fills the cavities of large Orthocerata. It pro- 

 ceeds from the Hudson River formation in Guelderland, near Albany, and occurs 

 on the surface of a spring and issues from the Utica slate on Great Manitoulin 

 Island (Lake Huron). The Niagara limestone sometimes affords traces of it; 

 and so also do the Medina red shales. 



The Corniferous beds of the Devonian afford petroleum at Black Rock in the 

 Niagara River, where it occupies cavities in fossils ; and, in sufficient abundance 

 to be an object of commerce, at Enniskillen in Western Canada, near which place 

 there is, over the surface, a deposit of solid bitumen or mineral tar, half an acre 

 in extent, probably derived from the limestone beds below. 



The Marcellus shales, or lower part of the Hamilton group, and also the upper 

 part of the same, contain occasionally concretions which enclose petroleum. 

 The rocks of the Chemung period afford abundant oil-springs in Erie, Seneca, 

 and Cattaraugus counties, New York. The oil-wells of Pennsylvania and Ohio 

 are sunk in Devonian or Subcarboniferous sandstones, often descending through 

 overlying Carboniferous strata. Some of the most noted " wells" in these 

 regions are at Mecca in Trumbull co., Ohio, Titusville on Oil Creek in Penn- 

 sylvania, and near the Little Kanawha in Virginia. 



In the American Mesozoic, a liquid petroleum occurs in Triassic shales and 

 limestone at Southbury, Ct. 



