312 THE DESERT SANDSTONE. 



attention was specially directed to the subject and thenceforth I 

 have collected sands and sandstones all through the various 

 colonies. What with these and the aid of friends, thousands of 

 specimens have passed through my hands and have received what 

 attentive examination I could give them from the microscope. 

 Afterwards when travelling through the volcanic regions of the 

 East, I have collected numbers of specimens as well, besides 

 observing the manner in which the ash deposits accumulated and 

 how the different epochs of eruption were represented by strata. 

 I have now before me while I am writing, many specimens, not 

 only from the hundreds of craters in Java, both active and extinct, 

 but sand from the active craters of the Moluccas, the Philippines, 

 Celebes, the Linschoten Islands and Japan. The list of Javanese 

 craters alone would be a long one. 



All these sources of volcanic material however distant and 

 different in their extent, have produced volcanic sands which are 

 one in character ; though one mineral may have been present or 

 absent, or more or less abundant in particular cases, yet the 

 general result is the same. 



It may be necessary moreover to state" that sand is one of the 

 commonest and most frequent of volcanic emanations ; but sand 

 just like sandstone may mean many different things. Sand is a 

 term applied to finely divided particles of various different minerals; 

 such as quartz, felspar, the various compounds of silica with quartz, 

 alumina, magnesia, iron &c. Even when restricted to the siliceous 

 sands alone, the term has still a wide multiplicity of applications. 

 If the fine sand of a granite country for instance is placed under 

 the microscope, the quartz presents a peculiar aspect which a very 

 little experience enables one to recognise as belonging to that rock. 

 It has a characteristic ruggedness about it with cavities and 

 included crystals always of some size. There are sure to be crystals 

 of different kinds of felspar, with mica and perhaps hornblende. 

 But if the sand be recent, or in fact an ash, the quartz bears quite 

 a different appearance. It has vitreous inclusions, though these 

 are not always numerous, but innumerable gas-cavities; and nearly 

 every fragment has microliths or crystallites, which are microscopic 

 portions of very many minerals in different stages of development 

 from an amorphous state to a complete crystal. The oddest as well 

 as the most beautifully fantastic forms may be seen even in minute 

 broken pieces of stone. They frequently present crystal faces, 

 and from this the nature of many of them can be made out, and 

 generally this is the case with the great majority ; but some defy 

 all attempts to reduce them to a geometrical form. Thus there 

 are threads and beads, hooks and symmetrical arrangements of 

 dots and feathered fragments. Petrologists, without attempting 



