QUATERNARY FORMATIONS - THE DRIFT. 221 



composed of limestone, and is thoroughly water-worn, and frequently 

 shows an oblique arrangement. 



Interstratified with these beds of sand and gravel are bands of clay, 

 sometimes quite pure, but more frequently arenaceous. These are 

 usually finely laminated, most frequently in a horizontal direction. 

 Occasionally the clay develops to a stratum of several feet in thick- 

 ness, but more often it only forms narrow bands alternating with the 

 finer grades of sand, which are also more frequently laminated in a 

 horizontal direction than in the coarser kinds, showing that both were 

 deposited in comparatively quiet waters. 



An occasional large lowlder occurs in the sand and clay as well as 

 in the gravel. Small fragments of rock, usually subangular, are 

 sometimes seen in the clay. 



The formation is subject to rapid changes as it is traced laterally. 

 At one point the section may be composed almost wholly of fine sand 

 and clay, and within forty rods, these may be entirely replaced by 

 coarse sand and broad bands of gravel. Large lenticular masses of 

 sand, gravel, or mixed material, are not unfrequent. This formation 

 reaches a thickness of about sixty feet. 



From its nature this deposit has a very limited extent as a surface 

 formation. In the abrupt banlis of Lake Michigan, it displays itself 

 abundantly, as represented in plate VILl, which likewise shows its 

 relation to the overlying and inferior deposits. "Where it comes to the 

 surface, it displays itself very feebly, and is scarcely distinguishable, if 

 at all, at many points. It forms, where present, a narrow, irregular 

 belt between the surface occupied by the Bowlder Clay and that of the 

 Lower Red Clay. 



II. The Lowek Ekd Clay. 



Lying upon the formation just described, we find a massive clay de- 

 ^osii. It differs most obviously from the Bowlder Clay, in possessing 

 I deep reddish or purple color, which weathers at the surface to an 

 ashy drab, while the Bowlder Clay, although not infrequently reddish 

 or even purple, is usually blue or drab, and differs also in the great ir- 

 regularity of its coloration. Hence the formation in question is ev- 

 erywhere known as the " red elay." It likewise differs from the Bowl- 

 der Clay in respect to the rock fragments contained in it. In the 

 Bowlder Clay these are extremely abundant, and of all sizes, from 

 mere pebbles to those of many tons weight. In the Red Clay, where 

 they are not entirely absent, they are, with rare exceptions, small, sel- 

 dom exceeding six inches in diameter, and more frequently they are 

 mere hand specimens. The great ma;jority of these fragments are of 



