THE GLACIAL DRIFT. 



613 



In the Four Lake Coiintiy of Dane county the linear arrangement 

 is finely marked, its directions coinciding with the directions of the 

 glacial striae on the underlying rocks. Lakes Mendota and Monona, 

 and Lake Waubesa, in part, lie in N.E.— S.W. valleys, the first 

 named occupying two such valleys, which are partly separated by the 

 rock ridge of Picnic and MacBride's points. The valley of Lake Mo- 

 nona extends several miles to the southeastward beyond the lakes, 

 preserving its direction, which, like that of the two valleys of Lake 

 Mendota, is about S. 67° E., or parallel to the direction of the stri^ 

 to be seen at the large quarries west of Madison. Numerous other 

 similar valleys of varying size are to be seen in the same country, 

 some occupied by marshes or streams, others entirely dry. Narrow 

 detached ridges, lines of marsh, and the outlines of the formations 

 show the same arrangement, and the same coincidence with the di- 

 rections of the strife. 



Plate XXVI A is a- geological map of the Four Lake Country, and 

 is designed to show especially how the areas of the several formations 

 have been carved out by the glacial forces ; since the formations lie 

 one above the other nearly horizontally, the map is also to some ex- 

 tent a topographical one. It gives also the directions of the strise 

 observed at different points, and the lines along which they indicate 

 the glacial movement to have taken place. It will be observed that 

 the glacial strise vary in direction from • due south at the southeast 

 corner of the ma,p to nearly west at its northwest corner, and that 

 the linear outlines of the formation areas, lake valleys, etc., keep pace 

 with this change in direction. The Atlas map of Area D, which 

 shows also the marsh and stream directions, etc , and is on a larger scale, 

 as well as more accurately drawn, brings this interesting relation out 

 even more strikingly. 



It would be instructive to describe in some detail the different 

 linear valleys, ridges and outlines of this district, tracing their vary- 

 ing directions, but the space at command forbids this. It. may be 

 mentioned that in the town of Springfield a single narrow valley, 

 carved out in the Lower Magnesian to a depth of 100 feet, is to be 

 observed curving gradually westward to correspond with a slight 

 change in the direction of the strise on its sides. 



ISTorl hwestern Dane and eastern Columbia counties are level com- 

 pared with the district just described, but the linear arrangement is 

 very plainly marked in lines of marsh, streams and geological out- 

 lines, as will be seen readily from an inspection of the maps of areas 

 D. and E. Fig. 52 gives the shape of the area of Trenton limestone 

 which occupies the towns of York and Columbus, extending also into 



