364 | A. R. Horwood—Upper Trias, Leicestershire. 
the Star Brick Pit show a stage in which carbonate of lime was more 
plentiful than sulphate of hme. The occurrence of brine (see Water 
Supply) in some abundance in Triassic waters, evidenced also by the 
salt crystals, shows, as does the presence of lime combined as sulphate 
and carbonate and as pure lime, that marine conditions were not far 
removed from the lacustrine phase, or else that from the land side 
a different source was being tapped totally unlike the highly aluminous 
Red Marl or lacustrine phase. That Rhetic beds were being laid 
down further east during the Red Marl period here would account 
for such marine incursions. If water with brine and coarse sediments 
were swept westward temporarily they would naturally give a different 
result under abnormal conditions from the deposits in the typical 
Rheetic sea. 
The occurrence of beds of bitumen in the Lower Keuper Sanaa 
is an indication that either carbonaceous deposits were laid down as 
in the Coal-measures, or else that it was poured out by volcanic 
agency as a subsidiary lava-flow. But it is not usually held that coal 
is bituminous in this sense, so that the second view must be held. 
It has even been suggested that gypsum may have owed its origin to 
a similar agency, voleanic activity, the water causing the sulphur 
emitted to be precipitated as a sulphate of lime. Volcanic activity is 
known in the Permian to have been extensive, but to what extent, if 
any, in Keuper times is uncertain. 
The coloration of the rocks at present is a matter of difficulty. If 
the green colour was original or the red colour conveyed in chalybeate 
waters,’ the investment of each grain must have been by a movement. 
from below upwards to explain intervening green bands, unless these 
were bleached as each grey horizon was at the surface, as may be 
suggested, and it may then be said that the red intervals indicate the 
amount of submergence after each such bleaching.? Intimately 
connected with it is the difference of physical characteristics, 
composition, and specific gravity of the red and green bands (see 
Petrology). Variegation was due to two processes. Firstly, the 
grey bands were decoloured after being coloured red by organic acids. 
at the surface, being formed in shallow water over mud-banks and 
exposed to the air, where worms, possibly bacteria, etc., may 
also have played a part. This denotes oscillatory movements. 
Secondly, the sandstones heavier and containing more calcareous. 
matter may have been laid down at flood seasons as the grey bands 
probably were, but in this they were perhaps never submerged again 
after they were raised along the higher levels of the river-head. 
Being derived from a different source they differ in constituents. 
from the marls. 
The desert conditions described in connexion with Mountsorrel 
Croft, etc., all relate to granitic or syenitic rocks. Frost and heat, 
alternating with cold, help to disintegrate granite, and it is lable 
to split up into blocks. The sand thus formed accumulates as a 
talus. Even a slight wind will set up sand-blast action, causing 
polished surfaces. As we examine the eastern boundary of the 
1 Accepting Dr. Moody’s view. 
* Following deposition of red colour. 
