206 Wisconsin Academy of Sciences, Arts, and Letters. 



sands and gravels are often undulatory, and even strongly bil- 

 lowy, and the bowls and basins in it commonly have more than 

 usual symmetry. A not uncommon arrangement of this stratum 

 is found in an undulating margin on the flank of a ridge of the 

 main formation, from which it stretches away into a sand flat or a 

 gravel plain. 



Setting aside this, which is manifestly a secondary formation, 

 it is still true that gravel forms a large constituent of the forma- 

 tion. Some of the minor knolls and ridges are almost wholly 

 composed of sand and gravel, the elements of which are usually 

 very irregular in size, frequently including many boulders. But, 

 notwithstanding these qualifications, the great core of the range, as 

 sbown by the deeper excavations, and by the prominent hills and 

 ridges, that have not been masked by superficial modifications, 

 consists of a confused commingling of clay, sand, gravel, andhoulders, 

 of the most pronounced type. There is every gradation of material, 

 from boulders several feet in diameter, down to the finest rock 

 flour. The erratics present all degrees of angularity, from those 

 that are scarcely abraded at all, to thoroughly rounded boulders. 

 The cobble stones are spherically rounded, rather than flat, as is 

 common with beach gravel, where the attrition is produced largely 

 by sliding, rather than rolling. 



Stratification. — As indicated above, the heart of the range is 

 essentially unstratified. There is, however, much stratified ma- 

 terial intimately associated with it, a part of which, if my dis- 

 criminations are correct, was formed simultaneously with the pro- 

 duction of the unstratified portion, and the rest is due to subse- 

 quent modification. The local overlying beds, previously men- 

 tioned, are obviously stratified, the bedding lines being often 

 inclined, rather than horizontal, and frequently discordant, undu- 

 latory or irregular. 



The Source of the Material — This, so far as the range in Wis- 

 consin is concerned, admits of the most unequivocal demonstra- 

 tion. The large amount of coarse rock present renders identifica- 

 tion easy, and the average abrasion that has been suffered indicates, 

 measurably, the relative distance that has been traveled. The 

 range winds over the rock formations in a peculiar manner, so as 



