AQUEOUS TYPES 637 



have rehandled and assorted much sand and without doubt modified tlie 

 form of granules.-^ Subjected to the various agencies of weathering, a 

 bed of aqueous sand or a bed of sandstone derived therefrom^, such as 

 that referred to above in connection with the Escambia sand, may grad- 

 ually assume residual characteristics and be conveniently classified as 

 residuo-aqueous. The quartz grains will undergo but little change in 

 size, form, or condition unless organic acids are present, but they may 

 become much stained and rusted from contact with other minerals. They 

 may be relied on to indicate the aqueous origin of the bed and to thus 

 distinguish it from the simple residual type of sand. The cleavable and 

 decomposable minerals, when present, will be broken up and altered and 

 their original size, form, and condition lost. A glacio-aqueous subtype 

 of sand results when a glacier operates with sufficient vigor on a firm 

 sandrock originally aqueous ; the granules becoming mechanically crushed 

 will show more and more of the characteristics assigned to glacial sands. 

 Many of the granules would be expected to retain more or less trace of 

 their original rounded outlines not seen in ordinary glacial sands derived 

 from the crystalline rocks, and faceting and striation could probably be 

 detected on some of the coarser granules. In the case of such a glacio- 

 aqueous subtype of sand the rounded granules are becoming sharply 

 angular, while in the aqueo-glacial subtype previously referred to the 

 edges and angles of irregular granules are becoming subdued. 



Until acted on by some secondary agency, glacial, volcanic, and residual 

 sands are generally found near enough to their home locality, so that 

 their origin may often be inferred with reasonable certainty. In the 

 case of aqueous sands, hoAvever, they may be transported to such dis- 

 tances that their place of origin can be determined, if at all, only by the 

 most detailed study of the constituent granules. This problem was at- 

 tacked some fifteen years ago by Mackie, and his observations and con- 

 clusions reported on in the paper previously cited, "The sands and sand- 

 stones of eastern Moray." From a study of the inclusions present in the 

 quartz and feldspar granules and from the associations of minerals found 

 to be present in the loose sands and the possible parent beds, he was able 

 to make very plausible inferences concerning the origin of the grains of 

 certain modern and ancient sand formations of northern England.^^ In 

 the quarts grains three types of inclusions were recognized in that 

 region, which, with those grains in which they were absent, gave four 



21 See paper by Hovey, "Clearing out of the Wallibu and Rabaka gorges on Saint Vin- 

 cent Island." Bulletin of the Geological Society of America, vol. 20, 1909, p. 417. 



22 See also paper by Sorby (loc. cit). Proceedings of the Geological Society of Lon- 

 don, vol. xxxvi, p. 47. 



