16 B. M. Bnjdone — Further Notes on the Trimmingham Chalk, 



Chalk, and this is just what one would expect if, as is probable from 

 their unaltered condition, these boulders are of quite local origin. 



The exception above mentioned was a large boulder, quite 30 feet 

 high, immediately under the new hotel at Sidestrand. Unfortunately 

 this was overlaid by a soft bed full of water, which kept its surface 

 constantly obscured by a downwash of mud, and it was impossible 

 to collect from it. It has now been destroyed in the sloping of the 

 cliffs, or, if anything be left of it, it is turfed over and concealed 

 for good. I did get from the foreman of the works a promise to let 

 me know when they began to cut into the boulder, but the promise 

 was not kept, and the operation was carried out in my absence, and 

 a valuable opportunity thereby lost. One thing about it, however, 

 was not entirely obscured by the mnd, and that was the presence at 

 about 4 feet from the base of a bed of laminated marl some 2 inches 

 thick. This remarkable occurrence may mark the boundary between 

 the zone of Terebratulince and the Cromer Chalk (which is decidedly 

 identical in age with that now exposed near Norwich, and therefore 

 belongs to the zone of B. miicronata) . Some well-marked line of 

 demarcation seems not unlikely, as there is a considerable pal^onto- 

 logical break. Not only Rh. Beedensis but also Terebratida sexradiata 

 ai'e not uncommon in the Cromer Chalk, but still imknown at 

 Trimmingham, and Micraster cor-anguinum, which is abundant 

 (relatively speaking) in the Cromer Chalk, is so scarce at 

 Trimmingham tliat I have not yet found a fragment of Micraster 

 there, though Mr. Savin has two specimens, apparently from the 

 hard basement bed. There are also four very characteristic Upper 

 Senonian Polyzoa, which in the South of England are found in 

 the uppermost beds (with abundant specimens of Magas pumiltis) 

 of the B. mucronata zone, but which are not found at Trimmingham, 

 though the environment there must have been so very favourable 

 to Polyzoa that they might be fairly expected to occur there 

 if they still persisted in the English seas. I have described 

 and figured three cf these, which I cannot identify with 

 published figures. It so happens that I have not yet recognised 

 any of these three in the B. mucronata chalk of Norfolk, but the 

 fourth, Membranipora (? Homalostega) clathrata, is abundant in 

 the Cromer Chalk, and adds increased significance to the dis- 

 appearance of Rh. Beedensis and Terebratula sexradiata. Under 

 these circumstances I should be very chary at present of adopting 

 a zonal description of the Trimmingham Chalk which would allow 

 of the Sidestrand erratics containing Bh. Beedensis being included 

 with it. Of course, if the great erratic was representative of the 

 cliff from which the other erratics were derived, it would be quite 

 conceivable that the marl band should be the boundary of the two 

 zones, and the mixture of Pentacriniis and Bh. Beedensis in the fossils 

 obtained be due to the presence of boulders both from above and 

 below the boundarj'. (Many puzzling records are probably due to 

 an assemblage of fossils gathered from a section containing the 

 boundary of two zones being regarded as a naturally contemporaneous 

 series, and assigned to the more prominent of the two zones.) 



