December 10^ 1915] 



SCIENCE 



835 



distance of over a quarter of a mile. Tlie 

 ledges and fragments are all of one type of 

 rock — a coarse granite gneiss — which also out- 

 crops in cliffs on the spur of Mt. Kinsman 

 immediately above the gorge of Lost Eiver, 

 and appears in a talus-like mass of blocks on 

 the steep slope between these cliffs and the 

 gorge. In many cases the blocks appear to have 

 been shifted very little from the ledges against 

 which they lie in tipped or overturned posi- 

 tions ; in other cases they are poised in such a 

 way as to make it seem likely that they have 

 been moved a considerable distance. The pot- 

 holes in question include several semi-cylin- 

 drical pits or alcoves of from 15 to 25 feet 

 diameter, and numerous holes and curved 

 channels of much smaller size, similar to the 

 potholes at Agassiz Basin, four miles down the 

 stream. The giant potholes are in no case com- 

 plete or even approximately so, but appear to 

 have been cracked up and dislocated by the 

 same agency which jostled the blocks gen- 

 erally, along the line of the brook. 



In his paper Mr. Sayles considered three 

 agents as possible factors in the breaking up 

 of the ledges and scattering of the blocks: (o) 

 frost action, (b) disruption by a moving 

 glacier, and (c) earthquake movements along 

 the line of the gorge, attended by rock falls 

 from the cliff above it. He considered frost 

 action inadequate because of the depth to 

 which the ledges have been ruptured and dis- 

 placed, and because in the lowest caverns there 

 are " cases where blocks which have slipped 

 from between other huge blocks in place have 

 left the upper and lower blocks entirely un- 

 moved in the solid ledge " ; he rejects disrup- 

 tion by the moving ice sheet for the same 

 reason, adding to it the circumstance that no 

 erratic material occurs among the blocks, and 

 that in one case a block has been shifted four 

 inches against the direction of advance of the 

 ice sheet. He adopts the theory of earthquake 

 movement and rock fall because of the close 

 association of the blocks of the gorge with the 

 inclined heap of blocks on the overhanging 

 slope, on the one hand, and with the cracked 

 and torn ledges beside the stream on the 



other ; because of lateral movements among the 

 blocks, of the pell-mell manner in which they 

 are heaped, and because of " smooth slicken- 

 side-like patches." It is conceived that after 

 the potholes had been excavated, by a large 

 glacier-fed torrent heading in the Kinsman 

 Notch, an earthquake, originating along the 

 line of the gorge, cracked the river-worn ledges 

 and jostled the fragments, shaking down 

 masses, at the same time, from the cliffs on 

 the hill near by. 



After looking over the phenomena at Lost 

 Eiver, it does not seem to me that the facts 

 warrant a preference for the earthquake theory 

 over that of glacial sapping and frost action; 

 nor do I feel convinced that the "giant pot- 

 holes " are products of torrent action. My 

 reasons are these: (a) Positive evidence of 

 earthquake movement seems to be meager if 

 not wholly absent. I did not see the " slicken- 

 side-like patches " mentioned by Mr. Sayles, 

 nor any other marks of faulting, although I 

 looked for them. The presence of one or two 

 such surfaces, however, even if hona fide 

 slickensides, would not necessarily prove post- 

 glacial faulting; for small faults, probably of 

 earlier date, are common throughout the White 

 Mountain region. If, as Mr. Sayles supposes, 

 the earthquake rift follows the gorge, it would 

 be natural to expect slickensides to be exten- 

 sively and distinctly developed, (h) The pres- 

 ence of the inclined heap of blocks at the foot 

 of the cliffs, near the head of Lost Eiver, does 

 not seem to me to demand an earthquake. It 

 is well known that rock falls may result from 

 other causes. One may suppose, for instance, 

 that during the evacuation of the notch by the 

 ice sheet, insecure masses of rock on the crags 

 above Lost Eiver, and angular fragments of 

 the same, occupying an englacial position in 

 the ice near by, would slide or fall to the 

 ground as soon as their support vanished, and 

 would produce a heap of blocks such as we see 

 here. In the transportation of these rock falls 

 to points beyond the foot of the cliffs, an in- 

 clined floor of stagnant, melting ice might 

 play an important part. It is also conceivable 

 that the production and accumulation of talus, 

 by ordinary processes, might proceed at an ab- 



