REPRESENTATIVES OF PRE-WISCONSIN TILL 32 I 



exposed. One of these sections (Fig. 2, Exposure 2) showed a 

 yellow and red oxidized till, almost identical in appearance with 

 the one previously described and lying in a corresponding posi- 

 tion beneath the ordinary buff till. The general character of the 

 exposure is shown in Fig. 3, in which the horizontal and vertical 

 scales are the same. 



In composition the lower till was similar to that of the Cen- 

 ter street exposure, being probably as high as 70 or 80 per cent, 

 in clay and quartz flour. Like the first, it was evidently derived 

 from the underlying conglomerate and showed the same quartz- 

 ite pebbles and the same yellow and red colors. The prevailing 



Fig. 3. — -Section showing the relations of the older and younger tills in the 

 Intervale Park exposure, Brockton. (Exposure 2 of Fig. 2.) 



color, however, was somewhat lighter, yellow and gray predom- 

 inating. Like the Center street exposure it was irregularly lam- 

 inated and separated from the overlying till by a sharp and dis- 

 tinct line of demarcation. 



With a view to comparing with other tills, samples of the ox- 

 idized till were collected and examined as to their composition. 

 In the following table the results of the examination are given 

 and compared with the immediately overlying till, and with the 

 till of drumlins in the vicinity of Boston : 



1. Highly oxidized clay-till x ... 



2. Ordinary till overlying the above 2 



3. Clay-till of Boston drumlins 3 - 



Attention is especially called to the clay constituent which in 

 the lower till is about four and a half times as great as in the 



1 Clay determined chemically, others estimated from physical examination. 



2 Estimated from physical examination. 



3 Average of sixteen careful physical analyses by W. O. Crosby, Boston Soc. Nat. 

 Hist., Proc, Vol. XXV., p. 124. 



