24 THE GEOLOGIST'S TRAVELING HAND -BOOK. 



5 c. Niagara. This group consists of two distinct members, a shale below 

 and a limestone above. 



The shale in New York constitutes a very uniform deposit, while the limestone, 

 from a thin concretionary mass in the east, becomes an extensive and conspicuous 

 rock, constantly increasing in thickness, in a western direction, even far beyond 

 the limits of that state. The cataract of Niagara is produced by the passage of 

 the river over this limestone and shale, and, from being a well known and 

 extremely interesting point, as well as exhibiting the greatest natural development 

 of these rocks in New York, this name was adopted for its designation. In this 

 vicinity, the limestone is 164 feet thick, with the shale beneath 80 feet thick. The 

 lower part of the Niagara group exhibits a great development of dark bluish 

 shale, which, on exposure, gradually changes to gray or ashen color, and forms 

 a bluish or grayish marly clay. In this state it is undistinguishable from the 

 ordinary clays, and its outcropping edges, when long weathered, are often 

 considered as clay beds. The Niagara is a very extensive formation, but its shales 

 are much more persistent and wide spread than its limestone member in the east, 

 but the limestone is more widely spread in the west. The gorge below the upper 

 falls at Rochester is the best place to study these shales. In an agricultural point 

 of view, this formation, like all limestones, is an admirable one. There is no better 

 soil than that of the Niagara about Rochester, New York . 



A silico-argillaceous limestone, hi New York, forms the beds of passage from 

 the soft shale below to the purer limestone above . It is of a dark or bluish color 

 when freshly exposed, but soon changes to light gray or ashen. These beds of 

 passage are succeeded by a dark bluish gray sub-crystalline limestone, of a rough 

 fracture, and separated into thin courses by dark shaly matter. The third member 

 is a coarse grained concretionary mass, in irregular layers, exhibiting a very peculiar 

 contorted appearance, as if much disturbed while in a semi-fluid or yielding 

 condition. The concretions often present cavities lined with crystals, or contain 

 the remains of some organic body. This is the surface-rock in West Avenue in 

 Rochester. 



The Niagara limestone is the great limestone which, in "Wisconsin, occupies 

 the peninsula between Green Bay and Lake Michigan, and then stretches southward 

 to the south limits of the state, and far into Illinois and Indiana. It will be noticed 

 in looking over the Guide, how many railroad-stations in the western states, just 

 mentioned are on the 5 c. Niagara, and how very extensive the formation must be. 

 Its general appearance is that of a regularly bedded brown or buff dolomite, with 

 occasional intercalations of beds of massive gray limestone. The quarries of 

 beautiful buff limestone at Athens and Joliet, Illinois, so much used in Chicago 

 for building-purposes, are in this formation. At Joliet there is 40 feet in thickness 

 of this buff and gray limestone. West and northwest of Chicago the Niagara 

 limestone is highly charged with petroleum, which oozes from the stone, blackening 

 the face of walls built of it. On Goat Island, at Niagara Falls, the petroleum 

 is also seen on the limestone in small quantities. In Michigan it is a grey 

 crystalline, rather fine grained, moderately fossilif erous, dolomitic mass, 218 feet 

 thick on Green Bay. 



In Western Canada the upper part of the Niagara limestone contains peculiar 

 fossils, and is called the Guelph, and in Wisconsin it is subdivided into the 

 4. Guelph, 3. Racine, 2. Waukesha and 1. Mayville beds. 



