328 MYRON L. FULLER 



pre-glacially decomposed rock and its accompanying soil, rather 

 than by the process of accretion, by which many of the later 

 deposits of till, such as drumlins, etc., were built up. 



4. The remnants of the early till are characterized by (<?) the 

 presence of 20 per cent, or more of clay, (d) the presence in 

 some of the tills of 10 per cent, or less of pebbles, (V) a compo- 

 sition which is dependent almost entirely upon the underlying" 

 or immediately adjacent rock, (d) the decayed or disintegrated 

 character of its materials, (e) the presence of colors character- 

 istic of high oxidation, (/") its position in certain cases upon 

 deeply altered and practically unglaciated rock surfaces, and (^) 

 its distinct line of demarcation, both as to color and composition, 

 from the overlying till. 



5. The upper till, on the other hand, is characterized in the 

 region under discussion by [a) the presence of probably less 

 than 5 per cent, of clay, (b) the presence of 40 to 50 per cent, 

 of rock fragments, (<r) a composition often largely independent 

 of the immediately underlying rock and including numerous 

 far-traveling erratics, (d) slight oxidation, and (e) by its 

 unweathered and distinctly glaciated fragments. 



6. No evidences of a soil zone between the two tills have so 

 far been observed. 



7. It seems probable that there were comparatively few 

 localities in which the highly oxidized tills remained at the 

 time of the last invasion, for otherwise there should be more 

 traces of oxidized material, especially the colored clays, in 

 the later till. The early tills were probably largely eroded 

 during the later stages of the same ice sheet by which they 

 were formed. 



8. The action of the ice of the last advance in many cases was 

 to cover the earlier till remnants by a new coating of till, and 

 was protective rather than erosive in its nature. 



9. Nothing indicative of more than two general periods of 

 glaciation has been noted by the writer. The position of strati- 

 fied deposits between two tills identical in character, and of the 

 Wisconsin type, is probably to be explained as resulting from 



