330 THE EEGOLITH 



characteristically distinct, gradually pass into one another.''^ 

 These types are : 



1. Normal, angular, fresh-formed sand, as derived almost 

 directly from granitic or schistose rocks. 



2. Well-worn sand in rounded grains, the original angles 

 being completely lost, and the surface looking like fine ground 

 glass, 



3. Sand mechanically broken into sharp angular chips, show- 

 ing a glassy fracture. 



4. Sand having the grains chemically corroded, so as to pro- 

 duce a peculiar texture of the surface, differing from that of 

 worn grains or crystals. 



5. Sand in which the grains have a perfect crystalline out- 

 line, in some cases undoubtedly due to the deposition of quartz 

 over rounded or angular nuclei of ordinary non-crystalline sand. 



The material of most beach sands is largely quartz, though 

 not invariably so. Those of the Bermudas and other coral 

 islands are, as a matter of necessity, calcareous. Those of isolated 

 deep-sea islands like the Ilawaiians, are derived in part from the 

 volcanic rocks of the islands, and in some instances are composed 

 almost wholly of minute shells of the size of a pin's head. These 

 last from their faculty of emitting a crunching sound when dis- 

 turbed, are known as ^^ sounding '' or ^'singing sands." 



The beach sand at Diamond Head, Oahu, is mainly of olivine 

 and magnetite granules, with smaller amounts of calcareous 

 matter. As usual, the grains in samples from the same level 

 are of fairly uniform dimension, varying from 0.5-1.0 milli- 

 metre, the larger forms being often fairly well rounded, while 

 the smaller may still show crystal outlines. The granules, even 

 in the same sample, however, vary greatly in the amount of 

 rounding they have undergone. Like the quartz granules from 

 the Florida beach next to be noted, these show conchoidal chip- 

 pings due to the shock of impact as one granule strikes against 

 another. 



The beach of Santa Eosa island, south of Pensacola, Florida, 

 is composed of clear white quartz sand of almost ideal purity. 

 The grains, though water-worn and with the lesser angles 

 rounded, are still in many cases angular, and of very uniform 

 size (about .5-1.0 millimetre), as shown in Fig. 36. These 

 granules offer a very beautiful illustration of Sorby's type No. 



* Proc. Geol. Soc. of London, Anniversary Address, Session, 1879-80, p. 58. 



