ORIGIN OF LATERITE IN NEW ENGLAND DISTRICT, N.S.W 237 



roofs of small caverns, produced by the expansion of gases in the 

 lava which had heaved its surface into huge bubbles or blisters. 

 The cavei'ns in the Emniaville basalts may have had a similar 

 origin and have been due rather to the distension of the surface 

 of the scummy lava, by imprisoned gases, than to the subsidence 

 of the fluid lava from overlying cooled crust or tuft?' 



Evidence of similar caverns was observed by me about three 

 miles beyond Laurel Hill, on the road from AdelongtoTumberumba, 

 At tliis point the hard stony basalt rings hollow for a distance of 

 several hundred yards, as the road approaches what seems to be 

 the remains of an old crater which has formed the source of the 

 lava stream. At this point, almost the highest in the range, a 

 semi-circular depression exists, surrounded on three sides by gentle 

 slopes of basalt, and open to the east. In the centre lies a circular 

 pool of water about live chains in diameter. The wdiole width of 

 the depression is from ten to fifteen chains. On the south side of 

 this old crater the basalt also rings hollow when struck, for a 

 distance of about ten chains down the road. There can be little 

 doubt therefoi'e of the existence here of lava caverns similar to 

 tliose just described in the laterite of Vegetable Creek. 



LIMONITE BEDS. 



Lenticular beds of earthy limonite occur locally in small de- 

 pressions in the laterite, their thickness seldom much exceeding 

 one foot. 



ERUPTED BLOCKS. 



Angular fragments of quartz-porphyry and granite, about one 

 foot in diameter, occur rather freely, principally near the edges of 

 extinct craters, and rest immediately on the laterite, in which, 

 however, I never found any of them embedded. 



MACROSCOPIC AND MICROSCOPIC CHARACTERS. 



From hand specimens it will be evident that the rocks, to 

 wliich I have applied the term laterite, are of very variable 

 character, ranging from undoubted tufts to decomposed scoriaceous 

 basalt and pisolitic ironstone. One of the most interesting speci- 

 mens of the tuff'is specimen No. 1 (c) which has been described by 

 me as follows* : — " In the Wesley ground, in Portion 40, 

 Hamilton, are four low conical hills, each of which is composed of 

 red, or yellowish-red, earthy laterite, the tuftaceous character of 

 the formation being more apparent here than elsewhere. Balls 

 of rotten pink lava, half-inch in diameter, are bedded in an 

 ochreish earth like plums in a pudding. Sharp, doubly-terminated, 

 quartz-crystals with bruised edges, and splinters of quartz as sharp 

 as broken glass, are scattei'ed plentifully through the mass of the 



♦Geology of the Vegetable Creek Tin-mining Field, p. 31. 



