Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/192

98 the current was reduced, the finer materials might be deposited. There is no evidence of any change of level during these deposits; and the river must have risen 50 feet at least in times of flood.

Fig. 33.-Sect on on Brading Down, Isle of Wight, showing blocks of Chalk in Gravel.

In conclusion I may mention that the beds described above as pluvial have been referred to by Mr. Godwin-Austen under the name of Head, or Subaerial beds; and I quite admit the propriety and importance of his terms in many respects; but I was obliged to use the term "pluvial," in order specially to introduce the notion of rain-water action, as I was treating of deposits made on slopes by the action of water (probably by a non-continuous action) and thus necessarily to be separated from the ordinary aqueous action, such as is performed by rivers, lakes, and seas; as well as from ordinary subaerial action. While the pluvial beds, as I have shown in my sections, pass down into the aqueous beds, they pass upward into Mr. Godwin-Austen's subaerial beds, and the stones which have been head at one time, and weathered by subaerial action, pass down into what may be termed pluvial beds, which in their turn are being constantly despoiled, and carried into the purely aqueous beds at lower levels. Although Mr. Godwin-Austen's term subaerial is an excellent one, I submit that it does not sufficiently define the kind of action for the purpose I have in view, and still less so for the paper I have prepared on the formation of valleys, and the denudation of the surface.

When the Crayford and Erith beds have been as fully examined as those at Grays, the numerical superiority of the Mollusca in the latter deposit (as shown in the following Table) will probably disappear.

The list of shells from Salisbury is principally on Dr. Blackmore's authority. The Grays list is compiled from Mr. Pickering's table, the Ilford one partly from Mr. Morris's; the remainder by Mr. A. Bell, who has revised the list, and omitted the doubtful species.