J. Lamplugh — Marine Shells in Boulder-clay. 513 



generally all that remains. As in the 'Basement' claj'-, these broken 

 shells are more plentiful in some places than in others, and where 

 these patches occur, the shell-fragments are scattered {not stratified) 

 throughout a limited area, whilst the surrounding clay is almost 

 destitute of specimens ; but nowhere are they nearly so plentiful in 

 this division as in the lower. 



In the South Cliff this ' Purple ' clay often shows indistinct lines, 

 suggesting stratification, and, indeed, in many places deserving that 

 name. 



Above the gravel already mentioned as often covering the 'Purple' 

 clay, lie variable and inconstant (as, indeed, nearly all the beds 

 above the clay are) beds of laminated sand and warp, sometimes of 

 considerable thickness. 



The surfaces of the laminee of both sand and warp are often, as 

 noticed by Professor Phillips,^ curiously waved, as though broadly 

 ripple-marked, and in one place I found the plates of warp pitted, as 

 though by rain. At one or two points in the South Cliff the sands 

 are curiously contorted and cross bedded. 



Overlying these beds is generally a mass of gravel, chiefly of 

 chalk, of a thickness varying in the South Cliff from half a foot to 

 four feet, but to the North of the town it is much thicker ; and 

 this, except where the fresh- water marls intervene, is directly covered 

 by the surface soil. 



Before proceeding to consider the conditions nnder which these 

 varying deposits were accumulated, it will perhaps aid the reader's 

 perception if I lay before him a summary of the results I have now 

 arrived at as to the division of the Drift in this locality, placed side 

 by side with the typical one set forth by Messrs. Wood and Eome in 

 the paper already alluded to. (See table on p. 514.) 



The origin of the beds lying above the ' Purple ' clay in this 

 locality is not difficult of explanation, being evidently due to 

 intermittent periods of stormy and quiet seas, of strong ocean 

 currents and placid lake-waters. 



But when we come to consider the conditions under which the 

 Boulder-clays, with their associated Sand-beds, were formed, es- 

 pecially with reference to the presence of shells in their midst, we 

 meet with many difficulties. 



On the one hand, the broken condition of the vast majority of the 

 shells, the worn character of many of the fragments, and the way in 

 which they are dispersed through the claj^, would lead us to suppose 

 that they had been carried hither with the rest of the materials of 

 which the clay is formed (as, indeed, evidently has been the case 

 with those in the 'Purple ' clay). 



On the other hand, the presence close by of a considerable body of 

 sand and shells (some with valves still united), the entirely unworn 

 character of some of the fragments, and the fact of sand still 

 remaining in the hollow of a single valve of Astarte, forbids the 

 supposition that such shells could have been drifted from any 

 distance, unless indeed we can imagine them to have beeu trans- 

 ^ Geology of Yorkshire, third edition, p. 82. 



DECADE n, — VOL. T. NO. XI. 33 



