THE FAUNA OF THE DEVONIAN FORMATION AT 

 MILWAUKEE, WISCONSIN 



The best, and until recently, the only known area of Devonian 

 rocks in Wisconsin lies immediately north of Milwaukee and 

 furnishes the Milwaukee hydraulic cement of commerce. This 

 rock, in the localities where it is exposed, is a limestone, rich in 

 magnesia, alumina, iron and silica. The best known exposure 

 is in the valley of the Milwaukee River, about half a mile north 

 of the present city limits. At this point many acres of the rock 

 are accessible, forming the bed of the river, and stretching away 

 on either side under alluvial and drift deposits, the latter of which 

 constantly increase in thickness with the distance from the river. 

 The formation is here about twenty five feet in thickness. Its 

 surface may be thirty feet above the level of the lake, which 

 lies a mile and a half to the east. There is a slight dip towards 

 the southeast. The formation rests upon a dark, porous lime- 

 stone supposed to be of Lower Helderberg age, without fossils. 

 Three miles further north, at the edge of Lake Michigan, is an 

 outcrop which rises slightly above the water level, and is about 

 twenty feet thick. A shaft sunk at this place discloses layers 

 corresponding to those of the lower twenty feet of the quarry 

 on the river. Five miles north of the latter and about three 

 miles further west there is a third exposure in a railway cut, at 

 .a considerable height above the river which flows near by ; but 

 the deep drift in the neighborhood of the cut has prevented any 

 determination of the extent of the formation in this locality. 



Within the past five years it has been found necessary to 

 make additional provision for the city's water supply. In carry- 

 ing out this provision a shaft was sunk to a depth of one hundred 

 and thirty feet at the edge of the beach at the head of North 

 Avenue, and from the bottom of this shaft a tunnel was bored 

 extending out thirty-two hundred feet under the lake. As a 

 preliminary to this undertaking test bores were made at a num- 



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