132 PROCEEDINGS COTTESWOLD CLUB 1903 
cliff, and are exposed for a thickness of about 98 feet, 
measuring from the end nearest the Red Lion Hotel. This 
thickness includes about 75 feet of red marl, rarely 
gypsiferous, variegated throughout, with zones of greyish- 
green and bluish marl, having angular and conchoidal 
fractures. These pass into light greenish-grey marls, 
having chiefly a conchoidal fracture, and rapidly weathering 
bluish-grey and white: in places they are coloured yellow 
by the downward infiltration of water containing iron 
oxide. Near the top of these “ Tea-green Marls” of the 
Geological Survey, is a somewhat hard band of marl, 
yellowish-grey and weathering whitish. Immediately above 
is a layer of soft green marl, of variable thickness, but 
seldom exceeding three inches. This layer is particularly 
conspicuous at the western end of the section where 
it is exposed in an excavation for collecting water. On 
the occasion of a recent excursion of the Club to the 
locality, the late Mr H. G. Madan, M.A., F.CS., 
enunciated his views with regard to the colouration of 
these “ Tea-green marls,” and subsequently kindly furnished 
me with some notes on the subject. “The iron derived 
from the older rocks would as a general rule find itself 
under such conditions as to form a persalt, such as the 
peroxide, or, in the presence of atmospheric carbon 
dioxide, the percarbonate ; and from these the red marls 
would derive their colour. If, however, much organic 
matter was washed down with the sands, this would com- 
bine with so much of the available oxygen that the iron 
would have to content itself with sufficient oxygen to form 
a protosalt only, and this would impart a green colour to 
the strata.” 
The Rhetic series’ commences with a mass of firm, 
black shales, containing a few fish-scales:* at their 
1 Wainlode Cliff is shown on Sheets 44 and 43 N.E. (Geol. Surv.) 
2 Full palaeontological details are given in the section (Table I.) at end of paper. 
