CAMBRIAN AND LOWER ORDOVICIAN. 125 



Poughkeepsie, N. Y. It is taken up again in New Jersey, and thence may be followed, with 

 some interruption, across Pennsylvania to Maryland, whence it extends as an almost continuous 

 formation across Virginia into eastern Tennessee and thence, with some interruption, into 

 Georgia and Alabama. On all this long line it forms the basal member of the Cambrian; and 

 wherever fossils have been found in it they belong to the Olenellus or Lower Cambrian fauna. 



The offshore or deeper-water deposits are represented by finer-grained sandstones, shales, 

 slates, and limestones. In southern Vermont they form the roofing-slate belt that passes into 

 New York, where the section comprises some 12,000 feet of shales, slates, and interbedded 

 sandstones, with more or less calcareous matter, either as brecciated conglomerate or as thin- 

 bedded, intercalated limestones. These extend, with some change in their character and 

 regularity of exposure, to the Hudson River in Dutchess County. Near StissingviUe, in this 

 county, the basal sandstone rests upon the pre-Cambrian and contains the OleneUus fauna. 

 A few remains of the latter have also been found in the immediate superjacent limestone. 

 The Middle Cambrian and Upper Cambrian faunas occur in bedded hmestones. As the quartz- 

 ite exposed on the eastern side of the limestones of the "marble belt" represents but a very 

 small portion of the great series of shales, slates, etc., of the Cambrian on the westem'side of the 

 "marble belt," it is probable that the lower portion of the limestone is of Cambrian age, the 

 same as in Dutchess County. This observation also apphes to the basal Hmestone in New 

 Jersey and Pennsylvania, where there is very little thickness of shales between the basal quartz- 

 ites and the limestone. 



The Beekmantown ("Calciferous") of the Champlain district was studied in 

 detail by Brainard and Seely/* whose paper contains maps and local structure 

 sections. They say: 



The term Calciferous was used by the older geologists of New York and Vermont to 

 designate the strata between the Potsdam sandstone and the Chazy limestone. The lower 

 boundary is well defined, as thp Potsdam sandstone has been long recognized an^ carries a 

 peculiar fauna. The«upper boundary, the base of the Chazy, is less definite; but we consider 

 it to be certain strata of sandstone, from 30 to 40 feet in thickness, described in the "Geology 

 of Canada," 1863 (p. 123), and found in the Champlain region in several locahties below all 

 other beds containing characteristic Chazy fossils. 



In our study of the rocks of the Champlain Valley we have been surprised at the develop- 

 ment of the Calciferous formation — at its vast thickness, its variety of rock, and its abundant 

 fauna. That the earlier geologists, who made explorations on this ground. Profs. Emmons, 

 'Adams, and Hitchcock, should have made such brief mention of this grand subdivision 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 difficult formation to decipher, because of its great thick- 

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

 beds of magnesian Hmestone. 



In our study of these rocks every important exposure has been visited on the Vermont 

 side of Lake Champlain from Pbihpsburgh to Benson, and most of those on the New York 

 side. Instead of a thickness of 300 feet for the Calciferous, as estimated in the Vermont report, 

 we find a thickness of 1,800 feet; instead of the four or five species of fossils there mentioned 

 we find over a hundred species, many of which are as yet undescribed. 



There are two locahties in which the entire sequence of Calciferous strata can be seen. 

 One of these is in eastern Shoreham, and was first discovered by Rev. Augustus Wing and 

 referred to by him as "the Bascom ledge." (See Am. Jour. Sci., 3d ser., vol. 13, p. 343.) It is 

 a great monocline 2 miles in width and 3 to 5 nailes in length, in which aU the Lower Silurian 

 rocks are seen overlying at least 200 feet of Potsdam sandstone. The strike is somewhat 

 sinuous and the dip varies from 9° E. to 38° E., but there are no abrupt changes in either 

 except at the northern or western borders. Much of the rock is covered with soil, but 

 exposures on hillsides, along watercourses, and in escarpments of cliffs are sufficient to reveal 

 the character and thickness of aU the members of the Calciferous formation. * * * 



