HARDWICKE'S SCIENCE-GOSSIP. 



13 



render the cretaceous matter on Haldon approxi- 

 mately (but not quite) as thick as at Blackdown. The 

 corals have been described by Professor Duncan. 

 (Q. J. G. S., Feb. 1879.) 



The angular flints, which are doubtless the result 

 mainly of sub-aerial denudation, presuppose a con- 

 siderable thickness of chalk, which at one time capped 

 l he greensand, but which has now vanished altogether, 

 with the exception of this coarser and insoluble resi- 



that in this way it obtained both its rounded pebbles 

 and its plateau features. It became in fact a plain of 

 marine denudation. Since that time however it has 

 been re-elevated several hundred feet, so that rain and 

 rivers have "writ their wrinkles" upon it, and have 

 produced a vast hiatus between the outliers and the 

 parent mass. 



In conclusion, let us sum up the record. I. We have 

 at the base, Trias, which was deposited probably 



^CCjOQGoc 



Fi?. 20. 



Fig. 



Fig. 16. Fig. 17. Fig. 21. Fig. 22 



Figs. 15-22.— Fossil Sponge Spicules, nil drawn on the scale of J 5 th to r^j„th of an inch. (H. J. Carter on " Fossil Sponge: 

 Spicules . . . from Blackdown and Haldon," " Annals a.id" Magazine of Natural History," for Feb. 1871, p. 1 59.) 



Fig. 23. — Gcrvillea auceps. 



duum. But sub-aerial denudation is not the only 

 physical change indicated by the flint gravel, for upon 

 the surface and for about a foot beneath it rounded 

 pebbles occur, not only of flint, but also of rocks 

 foreign to the bed itself, such as quartz and grit 

 derived from the Palseozoic rocks adjoining. 



Here then again come traces of aqueous action. 

 And the natural inference seems to be that the bed 

 had sunk again beneath the surface of the sea, and 



Fig. 24. — Ammonites varicosus. 



in an inland sea. 2. Subsidence, and more truly marine- 

 conditions, when the Lias was deposited. 3. Eleva- 

 tion, tilting, and denudation, prior to the depo- 

 sition of the greensand. 4. Subsidence, and the com- 

 mencement of the deposition of the greensand beds. 

 5. Elevation, or silting up, or both, until shallower- 

 water and littoral conditions favoured the growth of 

 encrusting corals and polyzoa. 6. Subsidence again 

 till oceanic conditions prevailed, and chalk beds of 



