300 GEOLOGICAL EXCURSION TO THE ROCKY MOUNTAINS. 



At Milwaukee the surface formation is the gray pebble clay of 

 Champlain age. Within the limits of the city Devonian (Hamilton) 

 strata occur. This is the only area of Devonian rock within the bounda- 

 ries of Wisconsin. The rock is an impure limestone, from which an ex- 

 cellent hydraulic cement is made. The Niagara limestone, upon and 

 against which the Devonian lies, is here of such a character as to 

 afford an excellent building stone, and is extensively quarried for that 



purpose. 



At Wauwatosa, also, there are extensive quarries in the Niagara 

 limestone, similar to those in Milwaukee. The gray pebble clay, of 

 Ohamplain age. extends somewhat west of Wauwatosa. 



Prom Wauwatosa to Pewaukee till (ground moraine) is well shown, 

 underlain by Niagara limestone. 



Pewaukee to Oconomowoc. Ahout midway between these two sta- 

 tions (from Hartland to Nashotan) the Kettle moraine is crossed, 25 

 and here its characteristic topography, its accompaniment of lakes and 

 its constitution, may he seen. Between these stations also the Mud- 

 son River shale appears from beneath the Xiagira limestone, but is 

 concealed by the drift. The Niagara limestone dips to the eastward, 

 and the Hudson River shale is the next subjacent formation and ap- 

 pears at the surface, except for the drift covering, us the Niagara 

 thins out to the westward, before Oconomowoc is reached, the (ialena 

 (Lower Silurian) limestone appears from beneath the Hudson River 

 shale, as the Hudson River shale appeared from beneath the Niagara. 

 The region about Oconomowoc is famous for its lakes. The moraine 

 crossed between Pewaukee and Oconomowoc is the joint product of the 

 Lake Michigan and Green Bay glaciers, the ice from the Lake Michigan 

 glacier moving westward and the ice from the Green Bay glacier mov- 

 ing eastward. The two iee movements met along the line of this 

 moraine, which is therefore an interlohatc moraine, terminal to two ice 

 movements in opposite directions. 



Between Oconomowoc and Columbus the ground moraine iinds one 

 of its typical phases of development. Particularly in the region about 

 Watertown, and northwestward from Watertown to Columbus, drum- 

 lins are well developed. The drumlins have here a northeast-south- 

 west trend. This corresponds to the direction of ice movement in this 

 region, as shown by the stria'. Associated with the drumlins are on- 

 drained or <U-drained depressions which have an extension in the 

 same direction as the drumlins themselves, between Watertown and 

 Columbus the underlying strata are the Trenton (bower Silurian) time 

 stone, the St. Peter's sandstone, and the Lower Magnesian limestone, 

 in the order named. The strata all dip slightly to the southeastward' 

 and each formation appears from beneath the one preceding. 



