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Suppose, further, that a part of the intermediate area were raised to within two or three hundred fathoms of the surface for anything that we know to the contrary, the change of level might determine the substitution of greensand for the "chalk"; while, on the other hand, if part of the same area were depressed to three thousand fathoms, that change might determine the substitution of a different silicate of alumina and iron namely, clay for the "chalk" that would otherwise be formed.
We have got off the oolites on to what is called the Oxford clay; and then, I believe, on to the Coral rag, and on that again lies what we are coming to now. Do you see the red sand in that field? Then that is the lowest layer of a fresh world, so to speak; a world still younger than the oolites the chalk world. But that is not chalk, or anything like it. No, that is what is called Greensand.
According to the old nomenclature, this subdivision of the chalk was called Upper Greensand, in order to distinguish it from those members of the Neocomian or Lower Cretaceous series below the Gault to which the name of Greensand had been applied.
On digging or boring below these, we ought to come upon the chalk, and below the chalk again, with its cretaceous congeners the greensand or the gault, we ought to meet the Weald clay and the Hastings sand.
Carpenter, that the red clay is the result of the decomposition of previously-formed greensand. At present there is no evidence that greensand casts are ever formed at great depths; nor has it been proved that Glauconite is decomposable by the agency of water and carbonic acid.
I think it probable that we shall have to wait some time for a sufficient explanation of the origin of the abyssal red clay, no less than for that of the sublittoral greensand in the intermediate zone. But the importance of the establishment of the fact that these various deposits are being formed in the ocean, at the present day, remains the same; whether its rationale be understood or not.
Contemporaneously with these observations, the indefatigable Ehrenberg had discovered that the "greensands" of the geologist were largely made up of casts of a similar character, and proved the existence of Foraminifera at a very ancient geological epoch, by discovering such casts in a greensand of Lower Silurian age, which occurs near St. Petersburg. Subsequently, Messrs.
Yearly they tumble in, and yearly are renewed, as the soft greensand strata are graven away, and what must have been once a long promontory becomes a group of fantastic pierced rocks, exactly like those which are immortalized upon the willow-pattern plates. Owing to this rapid destruction, the rocks of Biarritz are very barren in sea-beasts and sea-weeds.
Its clear waters pass from the oolite of the Cotswolds, by the blue lias and its fossils, the sandstone rock at Clifton Hampden, the gravels of Wittenham, the great chalk range of the downs, the greensand, the Reading Beds, to the geological pie of the London Basin, and the beds of drifts and brick earth in which lie bedded the frames and fragments of its prehistoric beasts.
In certain parts of the Morea, the age of these volcanic rocks is established by the following proofs: first, the lithographic limestones of the Cretaceous era are cut through by trap, and then a conglomerate occurs, at Nauplia and other places, containing in its calcareous cement many well-known fossils of the chalk and greensand, together with pebbles formed of rolled pieces of the same serpentinous trap, which appear in the dikes above alluded to.
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