TACONIC QUESTION IN GEOLOGY. 265 
VII—PALEOZOIC History or EASTERN NORTH AMERICA. 
$ 126. To render more intelligible the relations of the Taconian, Cambrian, Ordovician 
and Silurian rocks of eastern North America to each other, and to the older Primary rocks, 
we shall endeavour to present a sketch of the geological history of the region, based upon 
_the facts already set forth. At the beginning of Cambrian time, marked by the earliest known 
trilobitic fauna, there stretched along the eastern border of the great paleozoic basin, a 
great area of crystalline eozoic rocks ; the remains of which are now seen in the Blue Ridge 
and its eastern slope, from Alabama to Virginia, and in their northeastern prolongation 
through the South Mountain of Pennsylvania, the Highlands of the Hudson, the crystalline 
rocks of New England, and of the whole region of Canada, south and east of the lower St. 
Lawrence. Tothe north of the great paleozoic basin was a similar eozoic area, now repre- 
sented by the Laurentides, stretching westward to the upper Mississippi, and beyond ; 
and connected by low-lying portions with the insular mass of the Adirondacks. The 
evidences of similar eozoic islands are seen in parts of Newfoundland, northern Michigan, 
Wisconsin, Dakota, Missouri, Texas, etc. These eozoic lands, alike on the western, on the 
northern, and on the eastern shores of this early Cambrian sea, presented then, as now, 
portions of several great terranes, or series of crystalline stratified rocks, lying unconform- 
ably upon one another, or upon a more ancient gneissic floor ; and telling a long history of 
successive depositions, elevations and depressions, sub-aérial decay and erosion. These 
various groups we have briefly noticed in the second chapter of this essay. (§ 18.) 
§ 127. The local geographical conditions presented by different portions of north- 
eastern America during the long period when the depression of parts of the pre-Cambrian 
land permitted the deposition over its surface, of Cambrian, Ordovician and Silurian sedi- 
ments, next demand our attention. 
Eaton had already, previous to 1832, divined that the Calciferous Sand-rock which, 
underlying the Metalliferous or Trenton limestone, rests directly upon the Primitive gneiss 
along the western shore of Lake Champlain, occupies the stratigraphical horizon of the 
Sparry Lime-rock found farther eastward, at the summit of the First Graywacke ; and con- 
sequently that this great mass of strata, as well as the more ancient Transition Argillite, 
and the Primitive Lime-rock and Quartz-rock, was absent along the western side of the 
lake. Emmons, in 1846, sought to explain this deficiency, so far as the First Graywacke 
was concerned, by maintaining that this great group of strata, together with its overlying 
Sparry Lime-rock, is really the representative, or as he expressed it, is “a protean deve- 
lopment.” of the Calciferous Saud-rock. In other words, this magnesian limestone, having, 
according to him, a maximum thickness of 300 feet, between the Trenton or Chazy lime- 
stone and the underlying gneiss; on the west side of Lake Champlain ; is represented to the 
eastward, along the western base of the belt of Primitive rocks, in New York, New 
England and Quebec, by a vast accumulation of sandstones, conglomerates, argillites and 
limestones ; to which he assigned a thickness of not less than 25,000 feet. Subsequently, 
in 1853, he recognized in that portion of this great series which had been known as the 
Red Sand-rock of Vermont, the representative of the Potsdam sandstone; which he had 
previously found to underlie, in some parts on the west side of the lake, the Calciferous 
Sand-rock of his Champlain division. 
§ 128. These conclusions of Emmons as to the stratigraphical relations of the First 
| Sec. IV., 1883. 34. 
