to6 [Proc. B.N.C.F., 



occurrence has given rise to conflicting theories, and left 

 problems of interest and difficulty still to solve. 



The Alexandra Slate Quarry, in which the shell-bearing 

 deposits are well exposed, lies in an east by south direction, 

 about three hundred feet from the conglomerate at the top of 

 Moel Tryfaen. The deposits form a thick series of sands and 

 gravels, occupying nearly a quarter of a mile in linear extent, 

 and having an average depth of from nine to twelve feet, with 

 occasional exposures fifteen feet deep. They exhibit both 

 stratification and current bedding. Extending originally over 

 the whole top of the quarry, much of these deposits is now 

 cleared away, but, as excavations extend, fresh surfaces come to 

 light, and till the vexed question of Moel Tryfaen, the acknow- 

 leged crux of geologists, is satisfactorily explained, I think steps 

 should be taken to secure, in the interests of science, the 

 preservation of as much of their shell fauna as possible. 



In the section as shewn in the diagram, kindly made by 

 Miss Sydney Thompson from a small photograph taken last 

 August, you will observe boulder clay averaging about ten feet 

 in depth, overlying a deposit of sand and gravel of rather 

 greater thickness. The sand immediately under the boulder 

 clay is very fine ; the shells on the table were found in a layer 

 of coarse sand and gravel, from one to two feet in thickness, 

 near the figure in the diagram, who is pointing to the spot 

 where one of the turritellas was actually found. Below this 

 part of the section, a layer of soft clay intervenes before you 

 come to the slate beneath. In other parts of the quarry, 

 especially towards the south-east, from nine to twelve feet of 

 fine sand is found between the top of the slate and the surface 

 of the ground. The edge of the slate rock sometimes presents 

 a bent and shattered appearance. The shells and shell frag- 

 ments are fairly numerous, mostly water-worn, the most perfect 

 being generally those that, as pointed out by Mellard Reade, 

 are of a form most calculated to resist pressure. Besides 

 British types, these deposits have yielded Arctic and Scandi- 

 navian species. I am sorry I have no Arctic forms to show 



