﻿Vol. 6 1.] VARIEGATION IN KETJPER MAELS, ETC. 439 



drawn to the nature of the colouring-matter in the pale-green 

 (greenish-white) sandstones of Carboniferous age occurring in 

 Scotland. These occasionally exhibited the defect of staining to a : 

 red colour along the mortar-joints when used as building-material. 

 The action often took place with great rapidity. Some specimens 

 which came under the speaker's notice were conspicuously mottled 

 in a few days, after contact with calcium-hydrate solution in the 

 form of slaked lime. 



The Author, in reply, said that in the Pylle-Hill section, which 

 had been described by the late Edward Wilson, the Tea-Green Marl 

 passed insensibly into the varigated marl lying beneath, and was 

 apparently identical with the green portions of the variegated rock. 

 While it was true that the Tea-Green Marl was a relatively-thin 

 deposit, and that the variegated marls and Triassic Sandstone 

 formed in the aggregate strata of enormous thickness, it was not 

 necessary in consequence to assume that the former had undergone 

 colour-change. The percolation of chalybeate water from below 

 into a rock originally all green seemed equally or more probable. 

 At the present time, an inexhaustible volume of chalybeate water 

 existed in the Wealden area in the Isle of Wight, and this water was 

 being brought to the surface and used in the power-house of the 

 Electric-Light Works between Sandown and Shanklin. In earlier 

 geological periods, chalybeate waters were probably more common 

 than they are now. It need not be assumed that the chalybeate 

 water-level coincided with the uppermost red rocks, for the capillarity 

 of the mass would allow of an easy upward passage of the water. 

 He differed from Prof. Seeley in thinking that the appearance of 

 the Keuper Marls was entirely in favour of infiltration, and in this 

 connection might point out that the upper portions of the Tea- 

 Green Marl are undergoing colour-change through the percolation 

 of water carrying iron from above. 



With regard to Prof. Armstrong's remarks, he felt that he was 

 under a far greater obligation to that gentleman than was incurred 

 in the mere receiving of specimens. He had had the privilege 

 of discussing with him the various points which arose during the 

 course of the investigation, and he was deeply sensible of the help 

 which such an association had afforded. 



