CONCENTRATION SAND TYPE 649 



been described by Hovey as consisting of fibrous chalcedony about quartz 

 fragments or aggregations of very fine sand particles^ the concentric de- 

 posits taking place about the nuclei in hot silicious waters/"'^ 



This would seem the proper place to describe a type of sand resulting 

 from the secondary enlargement of quartz grains formed by any of the 

 preceding agencies. About the original granule as a nucleus a shell of 

 crystalline silica is deposited in optical continuity with that of the orig- 

 inal grain^ gi^iiig sharp, fresh crystal facets and edges and generally 

 showing the double, pyramidal terminations (see figure 6, plate 46). 

 This condition of the Sylvania granules was recognized as early as 1840 

 by Bela Hubbard, assistant on the Michigan Geological Survey,^^ but 

 without any attempt at explanation. This was probably the first recog- 

 nition in this country of this type of sand grain, although it had been 

 earlier noted in Europe by numerous observers and generally regarded 

 as of chemical origin. Sorby described similar grains in 1880 from the 

 i^ew Eed Sandstone of Penrith, Engiand,^^ and noting the impressions 

 due to the interference of contiguous grains, concluded "that the depo- 

 sition of crystalline quartz took place after the nuclei were deposited as 

 a bed of normal sand" (page 63). Similar grains were described and 

 figured by Irving from the Huronian, Potsdam, and Saint Peter forma- 

 tions of Minnesota, Wisconsin, and Michigan,^^ and the importance of 

 this action pointed out in the transformation of sandstones into quartz- 

 ites (page 224). Subsequently a paper on the subject of secondary en- 

 largement of quartz grains was presented to the Geological Society of 

 London by Wethered.^^ The secondary silica he regarded as having been 

 "extracted from solution by the molecular affinity between the silica of 

 the detrital quartz and the silica in solution" (page 196). A later refer- 

 ence to the subject and some clear figures will be found in Yan Hise^s 

 "Treatise on metamorphism"^^ (p^ge 619). All who have written on 

 the subject since the paper of Sorby was presented are agreed that the 

 growth of the granules has taken place in situ from water carrying silica 

 in solution and presumably more or less concentrated. The widespread 

 character of the phenomenon and the conversion of so many sandstones 



^^ American Geologist, vol. xiii, 1894, p. 223. 



59 Third Annual Report of the State Geologist, 1840. House Document No. 27, vol. il : 

 Senate Document No. 7, vol. ii ; also separately, No. 8. 



60 Proceedings of the Geological Society of London, vol. xxxvi, 1880, p. 62. 



ci Fifth Annual Report of the U. S. Geological Survey, 1885, p. 218. This paper con- 

 tains a list of references to the literature of the subject. See also earlier paper by 

 same author "On the nature of the Induration in the Saint Peters and Potsdam sand- 

 stones," etc. American Journal of Science, 3d ser., vol. xxv, 1883, p. 401. 



6- Quarterly Journal of the Geological Society of London, vol. xliv, 1888, p. 186. 



"3 Monograph XLVII, U. S. Geological Survey, 1904. See also American Geologist, 

 vol. xiii. 1894, p. 225, for short article by Calvin. 



