CALCIFEROUS GROUP. 31 



"Pictured Rocks" of Lake Superior, the "Dalles" of the Wisconsin, and the 

 " Chasm of the Au Sable" in New York are examples. 



59. Everywhere it is essentially an accumulation of sandstone and pebbles 

 from the adjacent Laurentian gneisses, granites and syenites, and Taconic quartzites 

 and schists, resulting from the disintegrating influences of air and water. It con- 

 tains ripple-marks, wave-lines, mud cracks, animal tracks, and worm burrows, which 

 evidence shallow seas and shore lines. The continent at the time of its deposit did 

 not have one twentieth its present area. There is nothing known to indicate the 

 climate was different then from what it is now, except so far as the relative differ- 

 ence of land and water surface would necessarily change it. Some species of fossils 

 prevailed over great areas, as Eyolithes primordialis, I/ingulepis pinniformis, L. prima, 

 Dicellocephcdus minnesotensis, D. osceola, and Ptychaspis minvda, and therefore become 

 somewhat characteristic of the Group. Though composed almost wholly of sand it was 

 slowly deposited. The sandstone is frequently charged with fossils to its full capac- 

 ity, indicating a formation almost as slow as marine limestone is now made. There 

 is no doubt that Calcareous mud was forming in the depths of the ocean at the same 

 time the sand was deposited nearer the shore, but no limestone group of the Pots- 

 dam age has been found, unless it exists in the Eureka district of Nevada. 



CHAPTER V. 



CALCIKEROUS GROUP*. 



60. THIS name was first applied by Prof. Eaton to a gray rock consisting of 

 lime and fine grains of sand, so intimately blended as to appear homogeneous. It 

 contains calcite and a sparkling surface, but passes into a carbonate of lime, con- 

 taining beds of magnesian limestone and a small amount of iron. The Group was 

 defined by Vanuxem in 1842, in the Geology of the Third District of New York. 

 He united the silicious layers above the Potsdam, the calciferous sand-rock, and the 

 fucoidal layers in one Group. The rocks consist in general of three varieties sili- 

 cious, magnesian, and carbonate of lime, with intermediate grades of composition. 

 They pass from compact to granular, and granular to porous, the latter having cavi- 

 ties lined with crystals of quartz, calcareous spar; or, instead of being lined, pos- 

 sessed of a single beautiful perfect crystal of limpid quartz, nearly filling the space. 

 Middleville and Little Falls are noted localities for these crystals, some of which 

 contain a fluid or anthracite, which enhances their value as cabinet specimens. The 

 structure of the rock is often oolitic, passing into thick layers having a concretionary 

 structure, as in agate. The typical localities are in Montgomery and Herkimer 

 Counties. 



At Chazy the following ascending section occurs: 



1. Silico-calcareous beds, more or less interspersed with sparry masses, 30 to 35 

 feet; fossils rare and cherty. 



2. Limestone, in which the plates of Cystideans abound, 20 feet. 



3. Dull, gray, earthy mass, without fossils, and passing into oolitic beds, 10 feet. 



4. Cystidean limestone, similar to the first though of a brighter red color, 

 15 feet. 



