656 W. H. SHERZER RECOGNITION OE TYPES OE SAND GRAINS 



what afraid might occasionally have to be reversed. I have very little doubt 

 myself of the successive derivations of sand from previous sands — the Saint 

 Peter from the Basal sands and the Sylvania from both — but I doubt whether 

 it can be proven by any means yet at hand. I have been in hope that we , 

 might find a grain showing two stages of history in some such way as this — ' 

 {a) rounding and deposition, {!)) secondary enlargement, (c) erosion and re- j 

 wearing of the edges cutting down the angles of the secondary growth, (d) ' 

 redeposition. In such a case one might be able to see the fact of there having 

 been a second period of wear on the grain, and I would consider such a thing 

 conclusive. But I haven't found anything even suggesting it. 



"Charles P. Berkey. ; 

 "Ketchum, Idaho, July 8, 1910." ^ 



"Great stress can not be laid on similarity of enclosures as to origin of sand, ' 

 because a lack of similarity might be due to the introduction of some partial 

 source, and, secondly, because similarity might be due to a common source. 

 However, so far as the samples sent me are concerned, there is no reason why 

 Sylvania might not be derived from the Saint Peter. In fact, the indications 

 are that way so far as they are of value. Both are mainly quartz. In both 

 (salt shaft base and Saint Paul, Minnesota) microcline or other feldspar rarely 

 occurs. In the Sylvania there are rhombs of carbonate which are, however, I 

 think, always on the outside. Quartz with hair-like needles of rutile are com- 

 mon in both. Lines of enclosures along planes, generally gas, apparently, but 

 sometimes fluid, with occasionally gas bubbles (Sylvania, 7 miles north of 

 Monroe, 7 feet down), also occur in both. Small enclosures which may be 

 identified as apatite and zircon occur in both. Tourmaline occurs in brownish 

 tinges, and some small, thin hexagonal folia, which may be biotite (Saint 

 Paul, about 10 feet below Trenton ; Fitchburg, Wisconsin ; Rockwood, 20 feet 

 down). In one grain from the Missouri Saint Peter there seemed to be a knee- 

 shaped crystal of rutile in quartz which I did not see elsewhere, and one grain 

 of the basal salt shaft was a crystal with much higher refraction than sharp 

 quartz, crystalline in form and colorless, which I did not identify. It may 

 possibly be celestite. There were, of course, unidentifiable enclosures, but I 

 saw nothing in one set of sands characteristically different from the other 

 set of sands, nor was there anything in the way of grain such as hornblende, 

 epidote, monzonite, or similar materials which might serve as a characteristic 

 difference. 



"A. 0. Lane. 



"Tufts College, Massachusetts, June 2, 1910." 



