Chalk Bluffs of Trimmingham. 313 



he suggests that the mass must have been " undermined when 

 the crag was deposited, unless the boulder hypothesis is to be 

 preferred "*. 



Mr. Fisher has recently described in greater detail the 

 cavities he discovered in the chalk f ; but he still hesitates to 

 draw the inference which their existence seems naturally to 

 suggest. If they were sea-formed caves, as their position, 

 shape, and contents appear to indicate, and if (as he believes) 

 " they were formed and filled in the interval between the forma- 

 tion of the bluff and its envelopment in Boulder-clay," surely 

 this is almost sufficient to prove that the chalk mass existed 

 as a cliff previous to the formation of the Lower Glacial series. 

 I cannot think Mr. Reid is successful in explaining these caves 

 away as expanded cracks J. The cavity specially described 

 by Mr. Fisher has a much greater resemblance to the termina- 

 tion of a water-worn cave ; and since the chalk bluff is known 

 to have suffered so much in late years from the attacks of the 

 waves, it is quite possible that Mr. Reid has never seen any 

 such cavities as were visible up to 1868. Certainly none were 

 observable in 1875. 



Mr. Fisher finds a difficulty in the beds which rest on the 

 top of the bluffs, and which he thinks " were evidently lifted 

 up along with it ;" but he assumes that they belong to the 

 basement beds, or so-called Laminated series, whereas Mr. 

 Reid considers that they are a portion of the sands which 

 overlie the Till. And if he is correct, the difficulty vanishes ; 

 fjpr they are nearly on a level with the normal horizon of these 

 beds (as shown in Mr. Reid's diagram, he. cit. fig. 1). 



The undermined edge described by Lyell and the exis- 

 tence of these ancient caves are, to my mind, strong argu- 

 ments in favour of the view that the chalk bluffs were outlying 

 rocks or needles, the remnants of a chalk zone which once 

 formed a wide extent of land stretching far to the eastward, 

 and that they owe their preservation to the local disturbance 

 and arching of the strata, which gave them greater strength 

 and enabled them to resist the action of the waves. Against 

 their base were deposited the lowermost sands and clays of 

 the fluvio-marine series ; and as the area became gradually 

 submerged their pinnacle tops were broken off and carried 

 away ; and upon the truncated surfaces thus left were laid down 

 those later beds of clay and sand which are now seen in con- 

 tact with the chalk. 



It may also be pointed out that the Trimmingham bluffs 



* Principles of Geology, ed. 5, vol. iv. p. 86. 

 t Geol. Mag. dec. 2, vol. vii. p. 149. 

 X Loc. cit. vol. vii. p. 238. 



