324 THE DESERT SANDSTONE. 



and liquid mud had caused widespread destruction for leagues 

 around. The crater, it may be mentioned, is on an island which 

 was at the time of my first visit partly covered with vegetation. 

 But after the eruption, all this was devastated, and the forest 

 entirely burnt and destroyed. For this I must refer readers to my 

 account of the Volcano of Taal in the Proceedings of the Linnean 

 Society of New South Wales, Vol. ii,, (2nd series) 1887, p. 685. 



The whole of the country round Manila for many leagues is 

 covered with a fine-grained deposit somewhat different in mineral 

 character from that of Rome, but evidently a volcanic sandstone 

 or tufa derived from ash. Of this the buildings and walls of the 

 city are constructed, for it forms a moderately compact sandstone 

 like that of Rome. It is very much altered in places both in 

 colour and its state of oxidation, yet a good many of the thickest 

 beds have accumulated since the Spaniards conquered the islands, 

 or about 320 years. Not many reliable records of the eruptions 

 have been kept ; but leaves of plants are found in the strata which 

 are not indigenous, but beyond a doubt had been introduced by 

 Europeans. 



When we are dealing with a completely extinct volcanic region 

 as in Australia, it is of course impossible to make a general surmise 

 as to the periods covered by such eruptions as those which 

 spread the Desert Sandstone over so much of the north and the 

 interior of Australia. They may have been not only lengthened, 

 but also separated by long intervals of rest ; quite sufficient for 

 the surface to have become loosely blown about by the winds, and 

 giving rise to those round-grained sandstones found in the Mary 

 River. The little change that has been effected in active volcanoes 

 during the historic epoch, makes one think that what we call the 

 volcanic part of our Tertiary era, represents a long duration of 

 time. But in any case we might expect great deposits of ash 

 ejectamenta of which the Desert Sandstone represents but a portion. 

 I may mention in conclusion that whatever differences there may 

 be between the sandstones of say Manila or Java and Australia 

 when they are long exposed to weathering influences, there are 

 always traces of a good deal besides pure siliceous sands. As a 

 rule, recent volcanic sands and ashes are darkened by masses of 

 small opaque fragments of black scoriae, sometimes magne.tite, 

 pumice and what may be black fragments of dolerite. The 

 abundance of these cinclery opaque particles in recent volcanic ash 

 is very striking, giving it a black igneous appearance which is 

 unmistakable. Such appearances do not certainly belong to the 

 Desert Sandstone, but there are traces of it. At any rate the 

 differences in the appearances presented by the sands of recent 

 volcanoes and that of the Desert Sandstone can be accounted for 

 by chemical metamorphism from weathering, to which the latter 

 has been exposed. 





