30 GLACIAL GKAVELS OF MAINE. 



washed gravel on the one side and with sedimentary clay containing bowl- 

 ders on the other. The term "bowlder clay" may still have its uses, to 

 describe certain disputed formations, but in New England it ought to be 

 replaced by the word "till." This word is short, convenient, and implies 

 no theory either as to the composition or the origin of the deposit. The 

 till constitutes what was known to the older geologists as the "drift" or 

 "unmodified drift." 



In Maine the most constant characteristic of the till is that it is com- 

 posed of drift fragments of all sizes, from the finest particles of clay and 

 rock flour up to the largest bowlders, all indiscriminately mixed together in 

 a pellmell mass, except that the lower layers contain more fine matter than 

 the upper and a riiuch larger proportion of distinctly scratched or glaciated 

 stones. In the area of sedimentary rocks in the northeastern part of 

 Aroostook County the till consists almost wholly of sand and clay, most 

 of the larger stones having been broken into their constituent grains or 

 ground into powder, so as to resemble a soil of preglacial weathering, and 

 over large areas bowlders are almost unknown. Although almost all of 

 the till has drifted toward the south and east, the distance traveled varies 

 greatly. On Matinicus Island I found fossiliferous bowlders of Oriskany 

 sandstone which must have traveled 140 or more miles. By count of the 

 stones large enough to be plainly recognized lithologically, I have found 

 that by far the greater number, especially of those in the lower part of 

 the till, were derived from rocks not many miles away. Repeatedly the 

 lower till has been seen to be derived chiefly from local rock, while the 

 upper layers were derived from a rock that outcropped not far north. On 

 the other hand, I have sometimes found near the bottom of the till much 

 matter from a distance. Apparently the relative proportions of near- and 

 far-traveled matter in the till vary, but I have been unable to discover the 

 laws and causes. Sometimes I have suspected that the till of two different 

 glacial periods is mixed, but have not been able to find the necessary field 

 evidence. That the character of the till changes rapidly as we pass from 

 slaty into schistose or g-ranitic areas is proved not only by count of frag- 

 ments but also by the general appearance and tlie pliysical properties of 

 the soil, and often by the vegetation. Thfi greater part of the till of Maine, 

 and especially the large bowlders, must on the average have drifted but a 

 few miles. 



