Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/285

1869.] WILTSHIRE HUNSTANTON RED CHALK. 191 "The specimen of Gault," Mr. Forbes writes, "is, properly speaking, a marl (not a clay), being a mixture of ferruginous clay with a considerable quantity of carbonate of lime. The iron contained in it is all in the state of protoxide, amounting to 5.96 per cent., which would be equivalent to 6.606 per cent, of sesquioxide (red oxide) of iron, or to 4.62 per cent, metallic iron. The Hunstanton Red Chalk contains more carbonate of lime and much less clay than the above; and all the iron it contains is in the state of sesquioxide (red oxide), which amounts to 5.96 per cent., or is equivalent to 5.28 per cent, of protoxide of iron, or 4.10 metallic iron in the substance; it consequently, notwithstanding its red, or what generally would be termed ferruginous appearance, in reality does not contain quite as much iron as the Gault does, which has no such aspect; there seems to be no objection, from a chemico-geological point of view, why these rocks may not be representatives of one another. If the Gault were subjected to any oxidizing influences it would assume the red colour of the Hunstanton rocks, as it does also by burning."

Summing up, therefore, the evidence brought forward, observing that the fossils of the Red Chalk agree for the most part with those from the upper portion of the Gault of Folkestone, that the red band of Hunstanton agrees in position with the Norfolk Gault as being below the Chalk and above the Carstone, that the presence of iron brings it into concord with the Gault of Kent, it would appear that the Red Chalk is the representative of the upper portion of the typical English Gault (as seen in the Folkestone Section), and not of the Upper Greensand.

If the Upper Greensand exist in the Hunstanton series, its place must be in the band b, which rests on the Red Chalk, and which is so abundantly stored with Spongia paradoxica and Avicula gryphoeoides.

Discussion. The President remarked that the vertebrae from the Red Chalk, noticed and exhibited by Mr. Wiltshire, were undoubtedly those of Plesiosauris latispinus of the Upper Greensand; but associated with these were other bones which he could not identify with any part of the skeleton of Plesiosaurus.

Mr. Etheridge spoke in confirmation of the author's views, referring especially to the Palaeontological evidence.

Mr. S. Hughes mentioned a boring near Hitchin where a hard sandstone, resembling Carstone, was found immediately below the Gault, the latter having a thickness of 280 feet.

Mr. David Forbes remarked on the similarity in the amount of iron present in rocks so dissimilar as the Red Chalk and the blue clay of the Gault.

Prof. Morris noticed the similarity of the Carstone of Hunstanton, and its equivalent beds, to the Hilsthon and Hilsconglomerat, especially in their containing abundance of pisolitic iron-ore. He then adverted to the marked difference of the Lower Greensand of the