CLINTON GROUP. 49 



to waves and currents which transported the materials only short distances. The 

 conglomerate indicates a shore-line and rapid deposition, and is almost non-fossilifer- 

 ous, though a few fragments of fucoids and shells, generally too imperfect for 

 definition, have been found in it. The sandstone, too, bears the evidence of having 

 been deposited near the land in shallow water, not only in wave-lines, rill-marks 

 about shells, and ripple-marked slabs, but in mud-cracks produced by sun-drying. 

 In all these respects it compares with the Potsdam, which separates the Taconic 

 from the Lower Silurian. 



§ 100. In the more argillaceous part of the sandstone, fossils are sometimes 

 fairly well preserved. The characteristic fossils are Arthrophycus harlani, both genus 

 and species being confined to this Group, and having a wide distribution, and 

 Idngulella cuneata, a strongly marked species. Saline springs are common throughout 

 the whole extent of these rocks, and brine is universally found by boring. The 

 brine is frequently impure from the presence of muriate of lime and iron. Carbu- 

 reted hydrogen gas rises in many places on the Erie Canal east of Lockport, and 

 at Gasport it was collected and used for illuminating purposes a half century ago. 



CHAPTER XIII. 



CLINTON OROUF 5 . 



§ 101. This Group was named from the town of Clinton, in New York, and 

 defined by Vanuxem in 1842 ; and re-defined by Hall in 1843 in the Geological 

 Survey of that State. The rocks have no uniformity in color or composition. At 

 the typical locality there is green and black-blue shale; green, gray, and red 

 sandstone, often laminated ; calcareous sandstone and red fossiliferous iron ore beds ; 

 at other places, it consists of shaly sandstones and shales of various colors, impure 

 limestones, conglomerates, and oolitic iron ore, with concretions. It occupies a 

 narrow belt of country in New York, commencing near Canajoharie, and stretching 

 westward south of Lake Ontario, resting on the Medina Group, with the greatest 

 width in Wayne County, and, entering Canada at Hamilton, extends west to Lake 

 Huron, appearing on Drummond, Manitoulin, Cockburn, and other islands, and 

 probably enters the Peninsula of Michigan with a thickness of less than 50 feet, 

 and rapidly thins out. The maximum thickness in New York is about 400 feet. 

 The two \ipper bands of limestone included by the New York geologists in the 

 Clinton Group, are now generally classed with the Niagara, as they possess no 

 fossils peculiar to the Clinton, and the shales which separate them thin out in their 

 extension into Canada. In its easterly extension from New York, outcrops occur 

 as far as Anticosti Island and Newfoundland. On Anticosti it is described as one 

 of the divisions of the Anticosti Group, which there includes the rocks from the 

 Hudson River to the Niagara, and has a maximum thickness of about 500 feet. 

 It occurs in the Appalachian chain as far south as Georgia and Tennessee, and in 

 crossing Pennsylvania develops a thickness of more than 2,000 feet. The Group 

 thins out before reaching the Western States, and is unknown except upon the 

 borders of the Appalachian and Laurentian elevations. It appears to have resulted 

 from the mechanical deposition of materials derived from land lying north and east 



