﻿Vol. 6 1.] ELEA WTKE BEDS IN NORTH-EAST YORKSHIRE. 457 



VI. Summary and Conclusions. 



A consideration of these sections yields several interesting results. 

 A perfectly- complete transition from the Lias to the Lower Estuarine 

 Series is seen only at Blea Wyke. Elsewhere the change from 

 Alum-Shale to Dogger is abrupt : in a few localities only do we find 

 some of the peculiar fossils of the Blea Wyke Beds, in the lower 

 part of the Dogger. In all sections are to be seen some signs of 

 unconformity, and in most cases this is clearly shown by the occur- 

 rence of a well-marked basal pebble-bed. 



It is plain that, except at Blea Wyke, the Dogger rests upon an 

 eroded surface of Upper Lias, usually on some part of the Ammonites- 

 communis Zone, but in different localities on somewhat different 

 horizons. In many places the Lias has been worn, by current-action, 

 into large hollows, and in these have been deposited lenticular 

 masses of sandstone. 



Besides the basal conglomerate, bands of similar rounded fragments 

 and concretions often occur at various other horizons. Such phos- 

 phatic pebbles always indicate shallow-water conditions, and are 

 generally associated with contemporaneous erosion, as in the case of 

 the Cambridge Greensand. 



Over the greater part of North-East Yorkshire there exists a 

 considerable break in the stratigraphical succession between the 

 top of the Lias and the base of the Oolites. The evidence shows 

 that at this time peculiar physical conditions prevailed, notably 

 shallow water and strong currents over a wide area. The explan- 

 ation of this state of things is probably as follows : — After the 

 deposition of the Lias there was a period of slow elevation, which 

 caused the newly-formed strata to be uplifted within reach of wave- 

 and current-action. But it appears that the northern half of the 

 district was more elevated than the southern, and that, as first 

 suggested by Mr. Hudleston l in 1873, the Peak Fault is partly of 

 pre-Oolitic date. This fault formed a submarine cliff, and in the 

 still water at its foot the Blea Wyke Beds were laid down. Even- 

 tually the upward movement ceased, the hollow below the fault- 

 scarp was rilled up, and the Dogger proper was laid down as a con- 

 tinuous bed over the whole area. 



The occurrence of pebbles of Middle Liassic ironstone in the base- 

 ment-conglomerate of the Wainstones is important, since it shows 

 that in some direction, probably towards the north, the uplift must 

 have been much greater. This confirms the idea that the lapse of 

 time between the deposition of the Lias and that of the Dogger 

 was greater than would appear at first sight, and that the apparent 

 conformity is, in Yorkshire, to a large degree deceptive. 



The movements that produced this period of uplift may be 

 regarded as the forerunners of those which, at a later date, produced 

 slight local unconformities in the Middle Jurassic strata of the Mid- 

 land Counties. These small uplifts are connected by Prof. Kendall 

 with repeated movements of the Charnian Bidge, and the same 

 influence may have extended into the North of England. 



1 Proc. Geol. Assoc, vol. iii (1872-74) p. 304. 



