C. E. Be Ranee — Deposition of Cretaceous Strata. 249 



Lyme Eegis the Lower Cretaceous rocks overlap lower and lower 

 Oolitic beds, in consequence of the latter rocks having obtained their 

 anticlinal and synclinal curves, the upward rolls of which were 

 worn into a plain of marine denudation sloping E.S.E. before the 

 deposition of the Upper Greensand, while both systems of faults 

 traversing the district are of later age than the Chalk. 



It would appear that the movement which resulted in the axes 

 and easterly dip was one of subsidence, probably commencing after 

 the Portland Oolite had become a land-surface, through the combined 

 action of deposition filling up the shallow sea-bottom, and by an 

 elevation sufficient to place a considerable portion of the Oolitic sea- 

 bottom above the waves, which area comprised probably, not only 

 that covered by the Purbecks, but a considerable tract to the west. 

 And that this subsidence, though sufficient to produce the various 

 axes and flexures, to submerge the area sufficiently for marine forms 

 to exist in Purbeck times, was not of very long duration, or of very 

 great extent, as the freshwater Wealden beds were immediately 

 deposited over the Purbecks. 



This axis of old rocks produced a great east and west distui-bance, 

 causing numerous shai-p narrow anticlinals and synclinals, both in 

 Westphalia, Belgium, France, Somerset, and Pembroke, in which 

 curves lie very long and narrow troughs of Coal-measures, extending 

 for many miles. Mr. Prestwich lays stress on the great thinning 

 out in a southerly direction of the "pre-Cretaceous Secondary rocks" 

 observed by Mr. Hull, the Great and Inferior Oolites having thinned 

 from 792 feet in Gloucestershire to 205 feet in Oxfordshire, and the 

 Lias and Trias from 1090 to 400 (?), and the Trias of Lancashire 

 from 5600 to 600 feet in Warwickshire ; and he shows that this 

 general southerly thinning out points to old pre-Triassic land, which 

 may well have been the old ridge of Palseozoic rocks running out 

 from the Mendips. There is, therefore, little doubt that the Palseo- 

 zoic rocks are overlaid unconformably by successive Triassic, Liassic, 

 and Oolitic beds, precisely as the latter are overlapped by various 

 Cretaceous rocks. 



The great east and west axis of disturbance is believed to be of 

 post- Carboniferous and pre-Permian age, or of which is precisely 

 the era to which Prof. Hull writes, "-The northern limits of the 

 Lancashire and Yorkshire Coal-fields were determined by the up- 

 heaval and denudation of the beds along east and west lines, while 

 the Coal-fields themselves remained in their original continuity 

 across the region now formed by the Pennine hills from Skipton 

 southwards." ^ 



In the paper from which the above observation is quoted, Prof. 

 Hull shows that the Lanca'shire Coal-field is traversed by three 

 systems of fault ; of which my own observations in the survey of 600 

 square miles of West Lancashire have given me many opportunities 

 of corroborating. Of these the latest has a direction nearly N.N.W., 



1 Prof. Hull, Eelative Ages of Leading Physical Features and Lines of Elevation 

 of the Carboniferous District of Lancashire and Yorkshire, Quart. Journ. Geol. Soc. 

 1868, p. 331. 



