22 PROCEEDINGS COTTESWOLD CLUB 1907 
Deerhurst—the only compound coral yet found in the Plerta-contorta- 
Shales of this country.* 
At the foot of the cliff, Mr E. Talbot Paris gave a summary of 
Dr T. G. Moody’s views on the variegation of the Keuper Marls. 
The colour of the Keuper Marls, like that of many rocks, is due 
to the presence of compounds of iron. The colour of the green marl 
is due to iron in the ferrous condition, and that of the red marl to iron 
in the ferric condition. It is well-known that ferrous compounds are 
usually green or blue, and ferric compounds red or brown, and gener- 
ally the former are fairly easily changed into the latter by exposure to 
atmospheric influences. Therefore, assuming that the marls were 
originally all one colour, it might be supposed that the red marl had 
been formed from the green by the action of air, and a consequent 
change in the condition of the iron from ferrous to ferric, accompanied 
by a change in colour. This is the view which was held at one time 
by many geologists. That it is not correct, however, is shown by the 
fact that the red marl contains just as much iron in the ferrous condi- 
tion as the green does; also, the green marl on weathering does not 
turn red or brown, but greyish-green or white. The ferric compound 
(ferric oxide) which causes the red colour, is over and above any 
ferrous compound, and masks the green colour. 
It has been suggested by Dr T. G. Moody? that this ferric com- 
pound was introduced through the agency of chalybeate waters. In all 
probability the whole mass of the Keuper marl was originally green. 
Chalybeate waters circulated upwards through them, and effected 
a change which resulted in the greater part of the marl being turned 
red owing to the introduction of ferric oxide. Certain bands and 
patches remained green because they were in a harder and more 
crystalline condition, and so were able to resist the action of the 
waters. 
After tea at the Red Lion Hotel, the President reminded the 
Members that it was the sixtieth anniversary of the Club, which they 
would be able to celebrate more fittingly at their two days’ meeting at 
Burford, on July 24th and 25th. 
1 R. F. Tomes, Quart. Journ. Geol. Soc., vol. lix. (1903), pp. 493-497- ° 
2 Ibid, vol. 1xi. (1905), pp. 431-439- 
