Vol. 68.] KETTPER MAELS AEOUND CHAENWOOD. 291 



Nevertheless, the beds which are inclined do not differ from those 

 which are horizontal, and the contacts of each one with the 

 Charnian rocks lie on a horizontal plane. 



(6) The red marl consists of an argillaceous mineral, fine sand, 

 and minute rhombs of dolomite. 



(7) The argillaceous mineral is a silicate of aluminium, potassium, 

 iron, and magnesium. It occurs as minute laths, with straight 

 extinction and having greater elasticity along the shorter axis. 



/x Eefractive index of Canada balaam. 



fifi Very high. 



Specific gravity . . . 2*40. 



(8) The grey bands are more porous than the red, and above 

 and below them the red marl is often bleached. 



(9) The grey bands consist of seams of several different rocks, 

 often including one or more current-bedded seams containing sand 

 coarser than that in the marl, and also one or more seams of 

 quartzose dolomite rippled and bearing salt-pseudomorphs. 



(10) The ripples mainly trend north-westwards, and are steepest 

 on the north-east side. 



(11) Every sediment contains garnet, zircon, tourmaline, stauro- 

 lite, rutile, and magnetite. Of these the garnet, tourmaline, and 

 staurolite are probably derived entirely from a distant source. 



(12) The heavy minerals are intensely worn, resembling only 

 those of desert sands. In some seams of sandstone the quartz- 

 grains exhibit eeolian rounding. 



Conclusions. 



Finally, the mode of deposition of the sediment is discussed, and 

 an interpretation of the geology is offered. 



It is suggested that the Upper Keuper accumulated in an inland 

 basin wherein evaporation greatly exceeded precipitation. The 

 basin was always partly dry and partly occupied by pools of stand- 

 ing water. 



Prevalent south-westerly winds were continually precipitating 

 moisture on the hills south and west of the basin, and from these 

 hills streams of fresh water were constantly pouring down into the 

 desert, often uniting into extensive sheets, which would sweep far 

 and wide over the desert, and frequently be completely desiccated 

 ere they reached any pre-existing pool. 



The grey bands of far-travelled coarser sediment were formed by 

 5^iese water-flows, and the quartzose-dolomite seams mark the 

 desiccation which ensued. 



The red marls were laid down in the standing waters which 

 were comparatively deep, although the repeated alternations o£ red 

 and grey beds imply that the distribution of these deeps must have 

 been continually changing, the alteration being brought about 

 partly by silting up and partly by evaporation. 



Q. J. G. S. No. 270. T 



