76 It. M. Bnjdone — Further Notes on the Trimmingham Chalk. 



inverted is made very probable by the fact tbat the seams of 

 0. lunnta up to and including that immediately below the thick 

 flint follow the same inverted course, a fact pointed out to me by 

 Mr. Bidder. Now it will be remembered that the 0. lunata chalk 

 was continuous across the gap, and that the gap was quite recently 

 fairly narrow, and though no bed of flint happened to occur in the 

 arch of 0. hmata chalk crossing the gap, I am convinced (and 

 Mr. Bidder is equally positive) that the thick flint in the bluff was 

 identical with the flint line at a corresponding lieight in the 

 'secondary bluff' (Fig. 14). If we are right, then the thick flint 

 was not involved in the inversion. That being so, we should expect 

 to find filling the gap which would otherwise be left between the 

 thick flint which continues more or less horizontal, and the beds 

 below which break away from it, an ai'ea of reconstructed chalk, and 

 this is exactly what does occur there. The sketch below will show 

 what is meant : — 



Diagram-sketch of the north-west face of bluff. 



/, /, /, flint bands ; o, o, o, seams of perfect 0. lunata in section. 

 -A, area composed of chalk crowded with comminuted 0. lunata and no other fossils. 



Now I think we are entitled to assume (until the contrary is 

 shown) that the inversion is a result of the same, or practically the 

 same, force which has so greatly tilted the beds which are not 

 actually involved in the inversion, for both the tilting and the 

 inversion must have been produced before the deposition of the grey 

 chalk on the upturned ends of the tilted strata, since neither the 

 tilting nor the inversion has affected the grey chalk, and that fixes 

 the tilting and the inversion as of late Cretaceous age. Evidently 

 all the beds now appearing in the bluff were tilted together, but by 

 the time the angle had been reached at which the uninverted beds 

 now stand, these beds must have been raised above the plane at 

 which the thrust was operating, and the lower beds, being still 

 in that plane, must have been foi'ced to part company with the 

 uninverted beds, no great matter, as the whole could by that time 

 have only been lightly consolidated, and turn under themselves. 

 This view conforms very well with Lyell's figure of the bluff when 

 it was about twenty times its present length. This figure shows at 

 the north corner a small area of chalk with a steep dip which 



