THE GLACIAL DRIFT. 621 



eastward from the high prairie of the next town to the west is strewn 

 with immense bowlders in a very striking manner, and the same thing 

 is to be observed twelve to fifteen miles further north, alonor the lines 



O 



of the Wisconsin Central and Green Bay and Minnesota railroads, 

 east of Am hers t Junction. Clusters of bowlders are very common, 

 even much further south, as in the central part of the town of Mar- 

 cellon, Columbia county, and in the S. E. qr. of Sec. 3, Deerfield, 

 Dane county, where the bowlders are scarcely more than ten feet 

 apart, over an area of some 10 to 15 acres. When these clusters oc- 

 cur, they are very apt to be mostly of one kind. Altitude has evi- 

 dently had no influence whatever on the distribution of bowlders, since 

 they are found on the highest and lowest parts of the country, indif- 

 ferently. East of Devil's Lake, in the towns of Greenfield and Mer- 

 rimack, they are found in abundance and of large size on the highest 

 est portion of the Baraboo bluffs, at altitudes of over 900 feet above 

 Lake Michigan. Bowlders are found, also, on the tops of all the iso- 

 lated bluffs that occur within the drift-bearing area. Very large 

 hornblendic erratics, for instance, are to be seen on the very summit 

 of the limestone bluff of the northwestern part of the town of Spring- 

 field, Marqnette county. This bluff lies on the top of the divide be- 

 tween the waters of the Fox and Wisconsin rivers, has a height above 

 its base of 200 feet, and a total altitude of 730 feet above Lake Mich- 

 igan. It lies on the western edge of the Kettle Range, and a mile or 

 two west, in a country 200 to 250 feet lower, the drift has ceased alto- 

 gether. 



Gravel makes up a large part of the drift accumulations, though not 

 so great a proportion as the sand. Two general kinds of gravel may 

 be noted, the coarse and the fine, the former occurring more especially 

 in those regions where the drift appears to take on a true morainic 

 character, forming knolls and ridges, and the sides of many of the 

 depressions of the Kettle Range, whilst the finer gravel is met with 

 commonly in the valleys of streams, or wherever a distinct stratified 

 arrangement of the loose materials is perceptible. The coarse gravel 

 is for the most part of limestone pebbles, with which are mingled 

 some pebbles of white chert, and some of various crystalline rocks, 

 which increase in quantity towards the north. The ordinary limestone 

 pebbles are of a white color, run from three or four to eight or ten 

 inches in diameter, are commonly oblong in shape, much rounded at 

 the ends, and often have one or two sides smoothed and striated. Not 

 unfrequently fossils are contained, indicating the origin of the peb- 

 bles, which is also to be inferred from their lithological characters. 

 The coarse unstratified gravel is widely distributed over all the region 



