306 R. Cooksey Burton — Yellow Sand* and Marl. 



so that the water carrying the sediment must have quite filled the 

 hollows. The secondary beds are found as much as 50 feet above the 

 outcrop of the ' Yellow Sands ', so that the underground water must 

 have risen to at least this height and have filled the joints, fissures, 

 and caverns in the limestone breccia. Some of the sand beds contain 

 angular blocks of breccia, which have doubtless fallen from the roof of 

 the cavern during the deposition of the secondary beds. The thrust- 

 plane mentioned above was seen to affect only the upper beds of 

 the lower limestone, while the beds beneath were unbrecciated ; the 

 Marl Slate is thus probably unaffected by this thrust-plane, being 

 several feet below it. We have seen that the Marl Slate must be 

 disturbed and fractured, and in order to account for this we may 

 assume the existence of a second thrust-plane beneath the first along 

 which the Marl Slate and possibly lower beds have been set in motion 

 and fractured. The section from the Tyne southwards shows many 

 interesting breccias, and at Trow Rocks evidence can be obtained 

 proving that at least two series of thrust movements, and possibly 

 three, have affected the Permian of this area. In the first place some 

 pieces of breccia contain within them angular fragments of breccia 

 produced by a previous thrust-movement ; the limestone was first 

 brecciated, and the breccia, having been cemented into a compact 

 rock, was subsequently broken up by a second series of movements. 

 Moreover, the breccia as a whole is traversed in some places by a series 

 of joints, reversed faults, and other slickensided planes of movement, 

 which may have been formed during a third movement of the beds in 

 a horizontal direction. The thrust-plane, which affects the Magnesian 

 Limestone and is seen dipping south at the north end of Trow Hocks, 

 probably crosses the Marl Slate somewhere to the south of Trow 

 Rocks ; the ' Yellow Sands ' in the pockets may therefore have been 

 carried up hj water from this point and not from a place immediately 

 below their present position ; it would then be unnecessary to assume 

 a second thrust-plane to account for this phenomenon, but the 

 occuiTence of the above-mentioned doubly brecciated rocks renders 

 it probable that there is a second thrust-plane in the Coal-measures or 

 in the Lower Permian beds. 



The whole question of the origin of marl pockets in the Magnesian 

 Limestone may be affected by the discovery of the above secondary 

 beds of 'Yellow Sands'. 



Bedded ' Yellow Sands ' in marl pockets have not before been 

 proved; moreover, the existence of pockets, as at Marsden, containing 

 marl and angular sand-grains renders it probable that many marl 

 pockets are of secondary origin due to solution of the limestone, and 

 the subsequent washing in of marl and the insoluble residue left on 

 solution of the limestone. Many marl pockets are, of course, original 

 and are particularly rich in Permian Gasteropods and Foraminifera ; 

 such pockets are known at Tunstall Hope and have yielded, among 

 others, specimens of Textularia and Turbo Taylorianus. 



In conclusion I desire to express my thanks to Professor Lebour 

 and Dr. "Woolacott for their well-timed criticism and encouragement. 



