288 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



Tiny rock basins sometimes form on the surface of granite 

 and other rocks, and some such are described by Geikie as 

 occurring in the southwest of England. The Kettles and 

 Pans figured by him in his text-book are of this nature. Sim- 

 ilar rock basins are abundant in the Sierra Nevada. After 

 rains they commonly contain water. They are often more or 

 less rounded in shape, and are from a few inches to a few feet 

 or more in diameter. It is evident in this case that these rock 

 basins are purely the result of weathering, the material 

 being blown out by high winds. Plate XXXIX represents 

 such a basin, the bottom of which was covered with about two 

 inches of coarse granitic sand. Its width is about three feet 

 and its depth six inches. This particular basin appears to 

 have originated from the disintegration of a dioritic nodule 

 enclosed in granite, the cavity thus formed being subse- 

 quently enlarged. Dioritic nodules in this granite can be 

 seen at many points in various stages of removal, they being 

 here softer than the enclosing granite. 



The following statement by Professor Chamberlin, of 

 the University of Chicago, was kindly communicated by 

 letter: — 



While I think the action of ice in scooping out rock basins, in the produc- 

 tion of cirques, and in the refashioning of valleys, has notable limitations in its' 

 extent, I believe it to be, nevertheless, a phenomenon of some importance. 

 The most satisfactory evidence which I have seen personally is in Newfound- 

 land, where on the summits of plateaus, basins have been excavated in sand- 

 stone in such a fashion as to completely exclude the agency of ordinary 

 stream action, and also apparently that of solution, since the rock was essen- 

 tially insoluble. Disintegration may have prepared the way for excavation, 

 but it had obviously not reached the full extent of the excavated basin, since 

 the bottom and sides were ragged with the fractured faces of sound rock. 

 These basins were not simply rasped out. The rock was obviously torn 

 away from its place in blocks. The basins are generally small, being a few 

 rods in diameter and a few feet in depth, but they seemed to be unquestion- 

 able examples of mechanical excavation. 



In Greenland I saw much evidence of mechanical disruption, but I do not 

 recall any specific cases of basin formation, yet this is not strange, as the 

 topography of the region I studied was, on the whole, unfavorable to that 

 class of action. 



I think that in most cases of this kind there must be something in the ante- 

 cedent topography to determine this particular kind of action. I suppose 

 that diffierential action might form a basin in the midst of a plain, but I should 

 suppose such action would be very rare. So far as my observation goes the 



