THICKNESS AND FAUNAL WEALTH OF THE CALCIFEROUS. 503 



its variety of rock, and at its abundant fauna. That the great masters of 

 geological science who made explorations on this ground — Professor Emmons 

 on the New York side of Lake Champlain, aud President Hitchcock on the 

 Vermont side — should have made such brief mention of this grand sub- 

 division must be attributed to the fact that they had wide areas to examine 

 and but brief time allotted them. The Calciferous is, moreover, a most dif- 

 ficult formation to decipher because of its great thickness, the absence of 

 fossils in most exposures, and the resemblance to each other of its various 

 beds of magnesian limestone. 



The formation is essentially one of magnesian limestone, interstratified 

 with bauds and masses of pure limestone, pure silicious sandstone, and mix- 

 tures of these; or a calciferous sandstone, from which the name came. 



Professor Emmons * gives the thickness as between 250 and 300 feet ; but 

 the upper part of his Calciferous has been transferred to the Chazy. Presi- 

 dent Hitchcock in the Vermont report f assigns it a thickness of 300 feet. 

 But section after section demonstrates a thickness of six times that amount — 

 that is, 1,800 feet. The Vermont report gives the number of fossils as four 

 or five, and in the subsequent pages mentions two more. A collection, not 

 as yet by any means complete, has afforded us over ahuudred forms. These 

 fossils can be best enumerated with the various horizons at which they 

 occur. 



Principal Divisions. — The formation is not nnfrequently marked by abrupt 

 changes in strata ; and from lithological aud faunal characteristics, a basis 

 may be obtained which may be helpful for study. The divisions may be 

 named A, B, C, D, and E, reading from below upwards ; and in this natural 

 order they will be described. 



Division A rests upon the uppermost member of the Potsdam. The rock 

 is a dark bluish-gray magnesian limestone, massive or sometimes in beds one 

 or two feet in thickness, more or less silicious, weathering dark, sometimes 

 with a tinge of yellow. Nodules of white quartz are abundant in some of 

 the higher layers, and near the top large masses of black scoriaceous chert 

 make their appearance. 



Thus far division A has furnished no fossils. It has a thickness of 310 

 feet. 



Division B is characterized by the presence of masses of nearly pure 

 reticulated limestone, weathering white, intermingled with light-colored 

 dolomite. The bedding is very obscure. Dolomite prevails in the lower 

 part, and again above the middle; the middle and upper portions being 

 nearly pure limestone. This pure limestone, like the Birdseye in flinty 

 compactness, breaks easily with a conchoidal fracture. 



Geology of New York, 1st-', i>. 106. 

 t Geology of Vermont, Vol. I, 1861, p. 270. 



