192 INDEX TO THE STEATIGRAPHY OF NOETH AMERICA. 



In the southern part of the Hudson Valley the Ordovician divides around thepre- 

 Cambrian of the Highlands. In the eastern area the strata are more or less metamor- 

 phosed ; they are described with the similar slates and schists of New England (below) . 

 The western area extends through Ulster and Orange counties to New Jersey .^^^ 



Ries ®^^ recognized in Orange County the Trenton limestone and the " Hudson 

 River slates." Of the limestone he mentions one occiurence near Newburgh Feiry. 

 The slates are widely distributed. 



In the western part of the county the formation is represented by interbedded shales and 

 red and brown or gray sandstones, while in the central part the slates and shales only appear. 

 The sandstone beds again come in toward the northeast. Conglomerates are occasionally seen 

 in the northeastern part of the county. * * * Fossils are rare but have been found at several 

 localities. * * * They show a mixed Hudson River-Trenton fauna. * * * These rocks 

 rest unconformably on the Cambrian limestones and gneisses and underlie younger rocks in 

 the same manner. Their thickness in this county is probably not less than 2,000 feet. 



K-L 18-19. VERMONT, NEW HAMPSHIRE, MASSACHUSETTS, AND CONNECTICUT EAST OP 



THE GREEN MOUNTAINS. 



The presence of middle Ordovician strata in Vermont, in continuation of the 

 Canadian occurrences, is probable, but their distribution is not known. They 

 probably lie in synclines, overthrust by Cambrian and below remnants of the Silu- 

 rian, which here, as in New Brunswick and eastern New York, is probably uncon- 

 formable to the older strata. The structure is much confused by folding, thrusting, 

 and igneous intrusions. In Canada immediately north of the international boundary 

 EUs^^^ has traced out the divisions of the "Quebec group" and distinguished the 

 belts of graptolitic slates of the Ordovician. (See pp. 132-134.) The southward 

 extension into New Hampshire and Vermont was described by Hitchcock ^^^' *^^ as 

 the Calciferous mica schist and the Coos group. 



In Massachusetts and Connecticut the upper part of the Stockbridge dolomite 

 is of Beekmantown, Chazy, and Trenton age and the Berkshire schist is assigned to 

 the general position of the "Hudson River" — that is, to Trenton and later Ordovi- 

 cian, the upper limit being indeterminate. 



Along the boundary between New York on the west and Vermont, Massachu- 

 setts, and Connecticut on the east extends the Taconic Range, the area of the 

 Taconic system of Emmons. Dana published the results of his prolonged study of 

 the structural relations and his conclusions as to the true order of the strata of the 

 Taconic Range in a series of papers in the American Journal of Science (1872- 

 1887).^'*'^^^ He also summed up the history and facts in the Quarterly Journal.''" 



The early discoveries of fossils by Wing (see p. 189) were followed by Wal- 

 cott's discoveries in the central Taconic area, which proved the Cambrian and Ordo- 

 vician age of the strata. Walcott**^ distinguished the rocks of certain areas as 

 "terranes" and concluded that terrane 3, the upper part of the Stockbridge dolo- 

 mite, was equivalent to the "Calciferous" (Beekmantown), Chazy, and Trenton lime- 

 stones of the Champlain-Hudson Valley and terranes 4 and 6 were of "Hudson" age. 



In Berkshire County, northwestern Massachusetts, lies Mount Greylock, which 

 is composed of the Stockbridge dolomite and overlying strata. Dale ^^ worked 

 out its structure and gives the following tabulation of the stratigraphy as deter- 

 nained by him, in comparison with other classifications : ' 



