240 PROCEEDINGS OF SECTION C. 



depth of eighty feet below the surface on a bottom of basalt, and the 

 shaft was sunk forty feet below that level in hard basalt without 

 reaching the underlying older gravels. 



At the lower end of the Vegetable Creek lead between the 

 Wesley Extended deep shaft and Mount Prospect, there is clear 

 evidence of the laterite being partly covered over by the newer 

 basalt, as on both the east and west sides of the gully which runs 

 northerly from the Wesley Extended shaft, the laterite can be 

 traced out-cropping from under the newer basalt for about a mile. 



This phenomenon recurs in the Wellington Yale Lead near 

 Deepwater, where laterite is interposed between the older and 

 newer sheets of basalt. 



(b) As regards the geological age of the laterite, I am inclined 

 to think that part of it is synchronous with the older basalt, and 

 part, possibly of an age intermediate between that of the older 

 and newer basalts. 



The age of the older basalts has been decided by Baron von 

 Ettingshausen,* on the evidence of the fossil plants in the under- 

 lying sedimentary beds, to be Eocene. 



As yet there is not sufficient evidence for assigning any particular 

 geological age to the newer basalt. 



PROBABLE ORIGIN. 



The above observations may be summarized as follows : — 



1. Much of the laterite in New England is clearly a fragmental 



rock of volcanic origin, being largely composed of lapilli of 

 basalt. 



2. Rocks of the preceding class pass insensibly through altera- 



tion into pisolitic ironstones and earthy clay ironstones, 

 the former variety being largely composed of secondary 

 magnetic iron, whereas iron is present in the other varieties 

 chiefly in the form of limonite. 



3. The laterite occurs in sheets roughly circular or oval, having 



a maximum thickness of forty feet. 



4. The laterite is developed chiefly around points of basaltic 



eruptions, and constitutes a great part of the material of 

 which some of the old craters are composed. 



5. Cavernous spaces occasionally intervene between the bottom 



of the laterite, and the top of the underlying basalt. 



6. Erupted blocks of Palaeozoic rocks are occasionally found 



resting on the laterite. 



7. The laterite underlies the newer basalt, and in some cases 



overlies the older basalt, in one case being separated from 

 it by a thin bed of gravel. Frequently the under surface 

 of the laterite rests immediately on the tertiary sedimentary 

 beds. 



* Contributions to the Tertiary Flora of Australia Mem. Geol. Survey, N. S. Wales, 

 ralaeontology, No. ii, 1888, p. 78. ("Sydney, 4to., Government Printer.) 



