G. TV. Lamplugh — The Yorkshire Boulder-clay. 63 



boundaries in the clay. Though the Boulder-clay itself generally 

 contains many shell-fragments., the inclusions are as a rule unfossili- 

 ferous ; it is an exception to this rule (2b) which it is the proper 

 object of this paper to describe. 



To finish my description of the section, the above-mentioned 

 Boulder-clay generally rests directly on the chalk-rubble, as shown 

 on the right in my section ; but towards the centre of the South Sea 

 Landing its base rises higher so as to admit the intervention of thick 

 sandy and silty beds (lb) that seem at first to be interbedded with 

 the rubble. The Boulder-clay thins out over these, till it finally 

 disappears, and the stratified beds above and below it then come 

 together for a short space as shown at G. 



This thinning out evidently takes place in a north-easterly 

 direction, as is shown by the reappearance of the clay after we turn 

 the angle of the bay at C. 



Above the shelly Boulder-clay lies a thoroughly-washed gravel 

 (3), with regular bedding well brought out by sandy seams. 

 It differs from the lower stratified beds in ' containing a very 

 much larger proportion of foreign pebbles, some of them of large 

 size; and indeed in many places it includes scarcely any chalk. Its 

 thickness varies considerably, changing even within the limits of my 

 section from 2 to 12 feet, while half a mile away on the opposite 

 side of the Landing, at Beacon Hill, the cliff section cuts across a 

 mound of sand and gravel about 80 feet thick, which I believe to be 

 an exaggerated local development of this same gravel. 



Shell-fragments,, small and well-rounded, may be detected in it, 

 but I look upon these as being as much " pebbles " as are the 

 fragments of Liassic and other fossils which it also contains. It is 

 evidently a re-assortment of the Boulder-clay material, either derived 

 from the denudation of the clay, or, more directly, from the laving of 

 the ice which carried and formed that bed. 



Capping the section we have a thick mass of brownish Boulder- 

 clay (4), much more homogeneous in character than the lower bed. 

 The thickness of this clay is about 25 feet, but in one or two places 

 a band of pebbles (4a) occurs 6 or 7 feet from the top of the cliff, 

 which may indicate a line of division. 



This upper clay is perhaps on the whole the most constant factor 

 of the Glacial series of Flamborough Head, though it thins away 

 and disappears in one or two places, as over the flanks of the above- 

 mentioned great sand and gravel-mound at Beacon Hill. 



The Shell-bed. 



I will now revert to the mode of occurrence of the shell-bed. 

 The chief portion of the fossiliferous deposit takes the form of an 

 irregular lenticular seam of greenish-yellow sand, about 24 feet long 

 and at its thickest part not more than four inches thick. This bed 

 is curiously crumpled and twisted among the surrounding clay, and 

 at either extremity it is drawn out into a mere contorted thread. 



The accompaning figure (Fig. 2), in which a part of the section 

 shown in Fig. 1 is enlarged, is intended to bring out these features. 



