PALEOZOIC TIME — LO^YEK SILURIAN. 495 



Eange, Utah, and the lower part of the Pogonip limestone, in the White Pine and Eureka 

 districts. 



To the Trenton period are referred limestone beds at the Big Cottonwood Canon, 

 over the Cambrian, part of the Pogonip limestone ; Prospect Ridge, Fish Creek Mountain, 

 etc., in the Eureka district, Nevada, and later Trenton limestone (Hudson epoch?) in 

 Lone Mountain, with 500' of quartzyte between the two (Hague, Walcott); beds at Silver 

 City and Upper Mimbres Mining Camp, New Mexico, referred-to Hudson epoch ; in South 

 Park, Arkansas Canon, etc. (Stevenson, Wheeler Exp., 1876); in British America, grap- 

 tolitic Utica shales in the Kicking Horse Pass (Can. Rep., 1886). 



In the Trenton, near Caiion City, Colorado, occurs the Harding sandstone, in which 

 Walcott discovered, in 1890, the plates of Placoderm Pishes, described on page 510. 

 Walcott gives the following section of the rocks : At the base is a reddish gneiss. This 

 is followed by 22 i' of reddish arenaceous limestone with thin interbedded layers of chert, 

 carrying fossils of Upper Cambrian type. Above this limestone lie 51' of pinkish arena- 

 ceous limestone, carrying OpMleta, Straparollus, etc., characteristic of the base of the 

 Lower Silurian, or the Calciferous fauna of New York ; over this a series of sandstones 

 (Harding sandstone) 101' thick, in which occur, along with an abundant invertebrate 

 fauna, the plates of the Placoderm Pishes. A massive bedded, gray, arenaceous limestone 

 succeeds the sandstone with a thickness of 110', and this is followed by a thin band of 

 Carboniferous limestone. 



d. Arctic region. — Lower Silurian beds have been identified on North Devon, Corn- 

 wallis, Griffith, west coast of King William Land, Boothia, in Probisher Bay, from Hall's 

 collections, on the shores of Kennedy Channel. (For a review of the facts respecting 

 Arctic geologj^ and a geological map, see G. M. Dawson's paper, Can. Bep. for 1886.) 



The Taconic system of Emmons. — The Taconic system was first announced by 

 Emmons in 1842, in his N. Y. Geological Report of that year, and pronounced pre-Potsdam 

 on the general ground of the kinds of rocks and the assumed absence of fossils. In 1844, 

 fossils having become known to him from beds at Bald Mountain, in Washington County, 

 N.Y. , that had been included by him within the Taconic, he divided the Taconic series 

 into the Upper Taconic, or that containing fossils, and the Lower Taconic. Later dis- 

 coveries proved that his Upper Taconic rocks were really the oldest. The rocks of the 

 so-called Lov-er Taconic were quartzyte, limestone, and schists in several belts, — situated 

 along and near the Taconic range on the western boundary of New England, in Berkshire 

 and eastern New York, and thence extending northward and southward, and also west- 

 ward to the Hudson River. Although the "Lower Taconic" rocks are metamorphic, 

 and coarsely so in Berkshire, they were afterward found at many points to. contain fossils, 

 and are now known to be mainly of Cambrian and Lower Silurian age. 



These discoveries were made as follows, and chiefly in the limestone : 1857 to 1861, 

 Vermont survey, under C. H. Hitchcock and A. D. Hager, Geological Beport., 1861 ; 1871, 

 A. Wing, the fossils of the Chazy from West Rutland, Vt., reported on by E. Billings in 

 1872 ; 1865 to 1877, A. Wing, fossils in central Vermont, of the age of the Calciferous to 

 the Trenton, reported in 1877 ; 1879, T. N. Dale of the Hudson age, from the slates near 

 Poughkeepsie, N.Y. ; 1879 to 1890, W. B. Dwight, fossils from Dutchess County, N.Y., of 

 Cambrian to Trenton and Hudson, and in Canaan, N.Y., 1886 to 1890; C. D. Walcott, 

 fossils of Cambrian age in the quartzyte of southern Vermont, almost down to the Mas- 

 sachusetts line, and in shales or limestone of Washington and Rensselaer counties, N.Y. ; 

 also Trenton or Calciferous fossils in the limestone of Bennington, Vt., and In Williams- 

 town, Mass., on the west flank of Greylock, and in Berlin, N.Y., the region of the original 

 Lower Taconic. Further, .L E. Wolff and Foerste have found Cambrian fossils in the 

 limestone of- Vermont, near Rutland, and elsewhere. 



It has thus been established that the Lower Taconic is a combination of Lower 

 Silurian and Cambrian formations, as already stated. The author's stratigraphical inves- 



