﻿Vol. 64.] SUBDIVISION"S OF THE CHALK OF TRIMINGHAM. 409 



point out how little evidence in favour of any particular hypothesis 

 can be drawn from these relations. Whatever the cause of the 

 occurrence of Chalk at Trimingham, it is hardly open to dispute 

 that at no remote period the cliffs reached to the present low-tide 

 level, and all the Chalk that we now see was wholly enveloped 

 in clay. Any clay that is now found overlying Chalk may be 

 equally well a remnant of this envelope, or a more recent overcreep 

 from the great masses on the foreshore squeezed out by the weight 

 of the cliffs behind : in neither case does it afford any argument 

 as to the erratic or other condition of the Chalk. In the same 

 way, the clay which separates the blocks of chalk may quite as likely 

 be occupying the bottom of depressions — possibly synclinal folds — 

 in the surface of a continental mass of Chalk, as be held to be a deep 

 bed of Glacial clay with erratics of Chalk embedded in it. 



I should like to take this opportunity of elaborating an argument 

 which I stated too briefly in the Geological Magazine. This is the 

 argument from the boring for the Mundesley Waterworks.^ In 

 this boring the top of Chalk in situ was found at 89 feet below 

 the surface. The point at which the boring was made is not more 

 than 80 feet above Ordnance-datum (which is roughly the half- 

 tide level), so that the top of the Chalk at the Waterworks was 

 just about at low-tide level. We have, therefore, at distances from 

 a body of Chalk undoubtedly in situ varying from 1 to 2| miles, 

 Chalk appearing at the same level in several huge masses which, 

 even if detached, must extend downwards to a considerable 

 depth, and rising to a maximum of about 40 feet above low-tide 

 level. Even standing entirely by itself, this fact would seem to 

 set up a jjrima-facie presumption that the masses in question 

 are themselves in situ, and when a number of other considerations 

 point to the same conclusion the presumption becomes very strong. 

 Prof. Bonney has suggested an hypothesis (Geol. Mag. 1905, p. 397 

 etc.) that the Trimingham Chalk consists of erratics brought by 

 floating ice ; but, quite apart from any other considerations, the 

 mechanical difficulties involved in the quarrying-out of any one of 

 the three principal blocks, and the formation and retention under 

 water during formation of the enormous volume of ice which would 

 be required to float off the smallest of these blocks, seem absolutely 

 prohibitive to the theory of transport by ground-ice, and there is 

 at present no evidence in the British Isles of the existence in 

 Glacial times at any point but Trimingham of a cliff of Ostrea- 

 lunata Chalk from which such supposed erratics could be gathered 

 by glacier-ice. 



Some idea of the mass of Chalk which may have existed here in 

 quite recent times, may be gathered by applying the measurement 

 of the Bluffs given by Lyell " to show how much Chalk has been 

 destroyed even since his day. Lyell states that the North Bluff 

 was 105 yards long. As the maximum width of the neck leading 



1 Geol. Mag. 1906, p. 125; A. J. Jukes-Browne, 'The Upper Chalk of 

 England,' vol. iii of the ' Cretaceous Eocks of Britain ' Mem. Geol. Surv. U, K. 

 (1904) p. 263. 



2 Phil. Mag. ser. 3, vol. xvi (1840) pp. 357 et seqq. 



