SAYLES: THE SQUANTUM TILLITE. 163 



tillite. Until some outcrop is discovered where cleavage is absent, or 

 much less than at any exposure yet found, it is not likely that many 

 pebbles with glacial striae will be found. 



The mud-flow idea. 



Stanislaus Meunier tried to prove that the till of Switzerland was of 

 mud-flow origin. He did not prove his theory for Switzerland and 

 if he had been familiar with the immense areas of till in North America 

 he might have come to a different conclusion. That till does flow under 

 the ice when full of water, no glacial geologists will deny. There is 

 no reason why it should not flow under such tremendous pressures, 

 and flow-structure in till is often found. (Meunier, 1899). 



The mud-flows most commonly known are composed of mud and 

 disaggregated rock. The rocks from which flows are most likely to 

 come are shales or slates or argillaceous schists. Granite and sand- 

 stone or conglomerate would not be so apt to flow even in a disin- 

 tegrated condition. Mud-flows of this kind require a rather steep 

 gradient, and are limited to comparatively small areas. The materials 

 in the tillite under discussion are fresh and angular, showing no weath- 

 ering, and are not of the kinds found ordinarily in mud-flows. There 

 is no evidence of a steep gradient in the Roxbury series. The area 

 of the tillite is more than 100 square miles, so far as known by 

 outcrops and allowance for folding. The total original area was 

 probably several hundred square miles or even more. 



The mud-flows of volcanic origin are usually composed of a large 

 amount of volcanic materials, such as pumice, ash, scoria, bombs, 

 lapilli, etc. They are also, ordinarily, of comparatively small dimen- 

 sions. In the tillite no such evidence of a volcanic mud-flow has been 

 found. 



The volcanic action, however, near the tillite horizon shown in the 

 lava flow at Brighton and certain other places, may have no other eft'ect 

 than to cloud, for many, the whole issue of the glacial origin of the Rox- 

 bury series. Torrential waters as well as mud-flows are common in 

 volcanic eruptions and some volcanic materials are found in the tillite, 

 although the quantity is negligible when compared with the non- 

 volcanic materials. In some regions glacial deposits are made up 

 chiefly of volcanic ejections. In Glaciers of North America Prof. 

 I. C. Russell quotes Dr. C. Willard Hayes as follows: — "The moraine 

 in front of the Klutlan is the largest accumulated by any of the inte- 

 rior glaciers. It is composed very largely of the white volcanic tufa 



