14"> Bulletin Wisconsin Natural History Society. [Vol. 8. No. ::. 



coast line, with the exception of about three miles near the mouth 

 of the Milwaukee River, is formed of clay banks of varying 

 height, rising in places to ioo feet, and hardly anywhere falling 

 to below 50 feet. The lowland at the river mouth has been mod- 

 ified out of all semblance by human hands, being in the city of 

 Milwaukee. The same is true of small parts of the high shore. 



The clay banks are of lacustrine origin. They rest generally 

 on the boulder clay, the top of which is, roughly speaking, level 

 with the present beach. The lacustrine clay contains few boulders 

 or pebbles, but is interrupted in many places by bands of pebbles 

 and sand, which indicate old temporary beach lines. To the north- 

 ward, the clay is exceedingly cohesive, baking in dry weather al- 

 most to the hardness of rock. But a few miles south of the city it 

 is much looser, mixed to a greater extent with very fine-grained 

 sand, and yellowish instead of drab in color. Near the Racine 

 county line, the boulder clay underlying the lacustrine is but little 

 developed, and in some places absent, so that there the bank rests 

 on a rather soft shale, which apparently is related to the Hamilton 

 cement rock found north of the city. 



Between the bank and low water line there is almost every- 

 where a strip of beach, of varying width ; while north of the city 

 there is also a series of terraces, filling former shallow bays. 

 Numerous ravines cut deeply into the bank. The area may there- 

 fore be divided into beach, bank, terrace and ravine. As the 

 conditions vary widely in each of these, each class will be sepa- 

 rately discussed. 



The beach may be subdivided into shingle, gravel and sand 

 beach, which of course grade into each other, especially by the 

 sand being deposited and kept in place between the cobble stones 

 and boulders forming the first class. Shingle and gravel beaches 

 are formed principally near the headlands, where die current is 

 strong enough to carry the sand along, while sand beaches are 

 formed in the bays. The shingle beach is not formed by deposi- 

 tion, but is rather the remnant of the boulder clay, the finer por- 

 tions of which have been carried away ; the width of the beach 

 varies from a few feet to about 20 rods, being widest in the most 

 sheltered places. At a few points, the cliff descends directly into 

 the water without any trace of beach. 



Erosion along the shore is exceedingly active, operating prin- 



