DKIFTS OF THE VALE OF CLWXD. 97 



Table (continued). 





I. 



II. 



III. 



IV. 



V. 



VI. 



VII. 



yiii. 



Balanus balanoides, Linn 



porcatus, Da C. (=B. sulcatus, 



DaC.) 







•if 





•if 

 •if 



•if 

 •5f 





■if 

 -if 



-* 



* 



Serpula (Pomatoceros) triquetra 





Paet IY. 



Alluvium and Surface-drift. 



Now we must briefly examine the still more recent superficial 

 deposits of the Yale. In treating of the drifts this is of great 

 importance, seeing that it is so hard to distinguish the re-sorted 

 newest beds from the undisturbed original deposit from which they 

 were derived. Even in the older rocks this is a common source of 

 error. The compact breccia composed entirely of fragments of 

 Mountain Limestone which sometimes makes up the Brockram or 

 base of the Lower New Red Sandstone in the Eden valley is often 

 almost undistinguishable from the parent rock. The surface of the 

 Lower Chalk broken up and reset has often been mistaken for the 

 solid chalk, until a line of angular flints showed that it was only 

 consolidated chalk-gravel. Re-sorted Miocene has been reported to 

 contain remains of man. But the re-sorted drifts almost defy 

 detection in most cases. "We have already discussed the characters 

 which help us to make out whether the glacial drift remains as left 

 by the ice, or whether it has been sorted by the sea ; so also, if we 

 know the district well, we may ascertain whether we have before 

 us the marine deposit or only some of it washed to lower levels by 

 rain, or worked down the hill by all the other agencies which 

 modify the surface-soil (see Morton, G. H., 'Nature,' Sept. 30, 

 1880, p. 511). 



It is clear that a long time has elapsed since the last of the St. 

 Asaph Drifts was left by the sea ; this is evident, first, from an 

 examination of the newer deposits which have been laid down on it 

 or after it. The various kinds of alluvium which have silted up 

 the lower or northern end of the Yale of Clwyd are all newer and 

 must have taken some time to form. We have already pointed out 

 that in the sections near Ehuddlan they are seen resting upon what 

 looks like St. Asaph Drift. 



So we come now to the Alluvial Age. Alluvium and rainwash 

 must, from the nature of the case, have been formed in every period 



Q.J.GkS. No. 169. h 



