LANDSLIDES OF MT. GREYLOCK 515 



The middle slide came first, and the large one to the north 

 next. The time of the occurrence of the large slide to the 

 south was not noticed, but all must have occurred within a few 

 minutes of each other. 



The mountain in this place is made up, above, of a mica 

 schist (Greylock schist), and, below, of a rotten micaceous lime- 

 stone (Bellowspipe limestone). The slope is covered with loose 

 talus and earth, upon which is a sparse growth of trees. 



The north landslide occurred at the road near the top of the 

 mountain, where the slide is about 50 feet wide, and extends for 

 1500 feet down the mountain side. It gradually widens until 

 at the base it is about 200 feet wide. 



From the above it will be seen that all of the conditions 

 were favorable for a landslide ; the steepness of the slope, the 

 fissile character of the rock, the loose material of the mountain- 

 side wet with the unusually heavy summer rain. All that was 

 needed to cause a slipping of this loose material was a large 

 quantity of water to add to the weight of the mass, and at the 

 same time act as a lubricant. The destructive force of the 

 water was caused by the natural drainage of an unusually heavy 

 rain, and by the water brought down and squeezed out of the 

 mass which slid down the mountain-side. There is no evidence 

 that a dam was formed. In the ravine through which the water 

 flowed the water was in places 25 feet deep, as shown by the 

 overflow. 



The removed material was not piled up with a backward 

 slope toward the mountain, as is usually the case, the great 

 quantity of water being sufficient to remove a large part of the 

 debris so that much of the rock and earth was carried to and 

 •deposited in the valley below. 



The landslide at Briggsville is more complex. Back of the 

 -woolen mills of Strong, Hewatt & Co., and on the west bank of 

 Beaver Creek, one sees stratified blue clay tilted at all angles 

 from a 90-degree to an almost horizontal position. A pier is 

 raised 4 feet and tilted to the west, and the dam to the north of 

 the mill is raised several feet on the west side. The tilted area 



