DRIFTS OF FLlMDOROUGn HEAD. 401 



slopes of the valley until it has reached the looser drifts of the huried 

 ravine, and these, yielding readily to erosion, have been withdrawn 

 through the cave, so that deep pit-like creux or " blow-holes " have 

 opened upwards into the ground near the clifF-edge, revealing excel- 

 lent sections of the drift. 



In the first of these (see PI. XIII. fig. 8) * the dark Basement 

 Clay (4), resting on rough chalk rubble (5), attains a thickness of 

 over 2b feet and contains many shell-fragments. Its upper surface 

 shows signs of erosion, and is overlain by 30 feet of gravel. The 

 upper half of this gravel is full of chalk, very rough and morainic 

 in texture, with numerous subangular, far- travelled, erratic blocks 

 of large size (3 6^); while the lower half is of much finer material, 

 either without chalk or with the rarest sprinkling of it (3 ¥). The 

 parting between these beds is conspicuously distinct, the upper 

 seeming to cut down into the lower. On the north side of the crenx 

 a band of brown Boulder-clay, thinning out southward (3 6~), comes 

 in between these gravels, and the same band may be traced in 

 another section about 300 yards farther north. 



The beach in this neighbourhood is thickly strewn with erratic 

 blocks, some of them of large size, there being fully four thousand 

 within 350 yards of the solitary chalk pinnacle known as The 

 Matron. These have evidently been derived chiefly from the rougher 

 portion of the gravel (3 h^) f. 



The gravels are overlain by the earthy red Upper Boulder-clay 

 (3), now the most constant factor of the sections, which reaches to 

 t3he top of the oM^. 



This creuoc is not shown on the six-inch Ordnance map, and seems 

 to have broken through since the map was made ; but the next, 

 about a quarter of a mile farther north, is marked thereon as 

 '' Pigeon Hole." 



(m) Pigeon Hole. — In Pigeon Hole thick sands underlie the Base- 

 ment Clay as at South Sea Landing. These are evidently confined 

 to the buried ravine, as they are not seen in the cliff-section above- 

 the outer mouth of the cave. A large boulder was for some time 

 visible in these sands in an inaccessible part of the pit-walls. 



The Basement Clay itself here splits up into layers of diverse 

 composition, the lowest consisting chiefly of reconstructed chalk, the 

 next of a remanie mass of Speeton Clay (Neocomian and Kimeridge), 

 still containing many of the characteristic fossils + of that deposit, 

 while the upper layers alone are of the normal type of this 

 Boulder-clay, containing, however, shell-fragments in greater abun- 

 dance than usual. Gravel-streaks in some places intervene between 

 these zones. Eough chalkless gravel overlies the Basement Clay, 

 and above it the Upper Clay caps the cliff. 



* See also J. E. Dakvns, Proc. Yorks. Geol. & Polytechn. Soc. vol. vii. (1879) 

 p. 126, figs. iv. & v., and ibid. p. 250. 



t See also ' The Larger Boulders of Flamborough Head,' pt. iv. in Proc. 

 Yorks. Geol. & Polytechn. Soc. vol. xi. (1890) p. 397. 



\ These fossils show that the clay has been shaved oif from the outcrop of 

 the series, as nearly every zone between the Kimeridge shale and the Red Chalk, 

 both inclusive, is represented. 



