GREEN SAND, the name given to two divisions of the cretaceous measures (q.v.), They are so called from the occurrence in some of their beds of numerous small green specks of silicate of iron, someth»es so abundant as to give a green color to them. The term is, however, far from being descriptive of the various included strata; it must be considered simply as a name. In some districts, especially On the continent, the green particles are entirely absent from the strata. On this account it has been proposed that the lower greensand should lie called Neocomian. because strata of this period are well developed at _Neufchatel (Neocomum), in Switzerland. The mineral structure or litho logical character of the upper irreensand is so like that of the lower, that it is scarcely possible to separate them when the intermediate gault is absent, except by their organic remains, which are very distinct; so much so, indeed, as to have caused the placing of the one series in the lower cretaceous group, and the other in the upper. It should also be noticed that the relative importance of the two divisions is very different; the lower greensand includes a series of strata that are of a value nearly equal to the whole upper cretaceous group, of which the upper greensand is but a subordinate member.
The upper greensand consists of beds of sand, generally of a green color, with beds and concretionary masses of calcareous grit, called firestone. The strata on the cliffs of the isle of Wight are 100 ft. in thickness. This formation is supposed to have been a littoral deposit on the shore of the cretaceous seas. While the chalk was being depos
ited out at sea, these sands were being laid down along the shore, contemporaneous with the chalk, although they appear inferior to it. Their position would necessarily result from the cretaceous sea widening its area, and as the shore submerged, the greensand would be covered with the chalk, and would appear as an older and under lying deposit. The beds of this period are rich in fossils, abounding especially in the remains of sponges, mollusca, and echinodermata.
The lower greensand consists.of a large series of more or less indurated sandstones and clays, with occasional til'snreonc beds. They attain thickness of 850 feet. The sands prsoonderate in the upper, and the clays in the lower portion of the formation.
Some beds of clay of considerable thickness, sometimes as much as 60 ft., are used as fullers' earth. The calcareous stone is a highly fossiliferous band of limestone, locally called Kentish rag, much used for building in Kent and Sussex. The formation was formerly known as the iron sand, because of the sands being cemented together by an abundance of oxide of iron; this gives them a reddish color. The lower greensand Con tains numerous fossil mollusca and other marine remains. It is a sea deposit resting on the fresh-water vvealden strata, and showing that at this period the sea made considerable encroachments on the dry land.