Correspondence — Mr. J. Lomas. 527 



■whetlier it represents the materials of the Milburn series mingled 

 with detrital matter from the seaward margin of the Borrowdale 

 volcanoes will probably long remain a matter of opinion. 



In conclusion I may state that I should be glad to conduct a 

 party of field geologists over the areas here referred to if the excur- 

 sion can be ai'ranged for the summer months. If Mr. Marr should 

 care to be of the party, so much the better. 



Edinburgh Museum op Science and Art, J. Gr. GrOODCHILD. 



IQth October, lb92. 



SHAPES OF SAND GEAINS. 



Sir, — It is interesting to find that my friend Mr. Reade admits 

 the rounded sands in the Glacial deposits at Moel-y-Tryfaen " may 

 be treated as erratics." 



This view has been held by many glacialists of the anti-submergence 

 school for years. In a paper read before the Liverpool Greological 

 Society in December last, I stated that under the microscope the 

 glacial sands found under the cliflFs bounding the Mersey were 

 almost undistinguishable from those on the shore. 



But this fact gives no support to the belief that marine conditions 

 obtained during the deposition of those sands. It does not follow 

 that the sands have been rounded by marine action at all. 



It is particularly unfortunate that Mr. Eeade should have cited 

 the sands " which he has been living on and working in as an 

 engineer for the last twenty-five years" as examples of sea-worn 

 grains. 



Not only is the shore skirted by sand dunes whose bases are 

 washed by the tide, but the grains themselves have most probably 

 been derived from the Triassic and Permian rocks which form the 

 solid geology of the district. 



The remarkable roundness of grain which characterizes many 

 beds in these formations is well known. 



Not less striking than the roundness is the uniformity in size of 

 the grains in some beds. Some agent has been at work which is 

 capable of sifting. 



Through the kindness of various friends I have received specimens 

 of sands from many parts of the Desert of Sahara. In one case I 

 ■ had examples from different depths at the same place. The under- 

 lying grains are small in size, fairly angular, and contain a large 

 proportion of ferruginous grains. The upper layer is composed of 

 larger grains, extremely well rounded and very uniform in size. 

 In wind-borne material we should expect a sifting due to the varying 

 resistances offered to the wind by the sand particles. 



" Desert sands," according to Mr. Eeade, " are of course out of 

 the question in glacial geology ; " but in the present case it is 

 possible that " desert sands " of a former period may not be " out of 

 the question " and the roundness of grain may have little importance 

 in Glacial Geology. J. Lomas. 



University College, Liverpool, 

 October \Wi, 1892. 



