126 DR. THOMAS STEREY HUNT ON THE 



The subdivisions there recognized by him in ascending order were : 1. Lower Potsdam ; 

 2. Upper Potsdam ; 3. Lower Calciferon.s ; 4. Upper Calciferous ; 5. Levis ; and 6. Phyllo- 

 graptns beds. The second and third of these were regarded by Billings as the represen- 

 tatives of the Adirondack Potsdam and Calciferous, while the Phyllograptus beds at the 

 summit were considered the equivalent of the Welsh Arenig, which belongs to the base of 

 the Bala group, or the second fauna. It is evident, as Billings declared, that we have, in 

 this great thickness in north-western Newfoundland, a much more complete sequence than 

 in the Adirondack region, where the Upper Potsdam, Calciferous and Chazy subdivisions 

 represent the whole succession from the ancient gneiss up to the Trenton limestone. 



§ 139. Keeping in view the great development of the Cambrian alike in the Cordil- 

 leras and in Newfoundland, as compared with the Cambrian of the Adirondack and Mis- 

 sissippi areas, we are better prepared to understand the remarkable type assumed by this 

 series in the Appalachian area, on the eastern margin of the American paleozoic basin, from 

 near the Gulf of Mexico north-eastward to the Grulf of St. Lawrence and to Newfound- 

 land, along the western base of the Atlantic or Appalachian belt. These Cambrian rocks 

 throughout this extent, wherever preserved, are characterized by great thickness and con- 

 siderable diversities in composition, due to the accumulation of mechanical sediments de- 

 rived from the disintegration and decay of the various groups of pre-Cambrian rocks which 

 made up the adjacent eozoic land. To this, and to repeated movements of the land during 

 and after the Cambrian period, they owe their complex constitution, their great volume, 

 their disturbed and faulted condition, and their unconformities. All of these characters 

 serve to distinguish them widely from the horizontal and comparatively thin quartzites 

 and magnesian limestones, their representatives along the northern border of the great 

 basin as seen in the Adirondack and Mississippi areas. It is this Appalachian Cambrian, 

 many thousand feet in thickness, which, as we have already seen, constitutes the First 

 G-reywacke of Eaton, the Upper Taconic of Emmons, the Quebec and Potsdam group of 

 Logan, and a large part of the original Hudson River group. 



§ 140. That the Levis limestones and Phyllograptus shales, found at the summit of 

 this series, mark the beginnings of the second fauna, has already been noticed, as well as 

 the fact that still higher strata, of Ordovician and Silurian ages, are found over portions of 

 this Appalachian Cambrian series, among the strata of which they have sometimes been 

 involved by subsecjuent movements. It will also be borne in mind, first, that this great 

 mass of 10,000 feet or more of diversified and folded Cambrian strata is soon exchanged 

 to the west for a far more simple type of but a few hundred feet in thickness ; and, 

 secondly, that erosion has removed this great series wholly or in part from over large por- 

 tions of its original area, particularly south of the parallel of 45° north latitude. 



§ 141. With these explanations before us, we are now prepared to consider the rela- 

 tions of the Cambrian and Ordovician series, in their two unlike types of the Appalachian 

 and Adirondack areas, to the Lower Taconic limestones. It has already been shown that 

 Emmons, in 1842, in his final Report on the Geology of the Northern District of New York, 

 defined, with the present names, the lower subdivisions of the New York paleozoic sys- 

 tem, from the Potsdam to the Oneida, both inclusive, to which he gave the collective ap- 

 pellation of the Champlain division. He at the same time proposed for the granular 

 quartz-rock and the granular lime-rock of Eaton, found in western Massachusetts, the name 

 of the Taconic system, which he followed Eaton in assigning to a lower horizon than 



