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



Again, patches of sand and gravel interstratified witli and sur- 

 rounded by the ' Purple ' clay, are to be found in many places 

 in the cliffs both to the north and south of the town, and these con- 

 tain no shells whatever ; whereas, as already mentioned, those in- 

 cluded in the ' Basement ' clay contain them in abundance, and this 

 I refer to as another argument in the same direction. 



In the tubes of the Dentalia, and under a perfect valve of an 

 Astarle, obtained from the sandy clays on the South Shore, was a 

 true coarse ' Crag ' sand, showing the character of the bottom on 

 which these shells lived. Parts of the sandy clays (already mentioned 

 as forming the upper portion of the 'Basement' clay), when dried, 

 greatly resemble the true ' Crag ' both in colour and composition, 

 having the same greenish cast and containing the same small black 

 cherty pebbles. 



From these facts, and others, furnished by the direction of the 

 beds where they disappear beneath the town, I think it is evident 

 that the ' Bridlington Crag ' forms a part of the ' Basement ' and not 

 of the ' Purple ' Boulder-clay series. 



The ' Purple ' clay, which forms by far the greater part of the 

 whole deposit along the coast, has been so often and so well de- 

 scribed, that it is almost needless to enter into special details 

 respecting it. It is of a dark purple to the south, and of a reddish- 

 brown to the north of Flamborough, and contains more and larger 

 rock-fragments than the ' Basement ' clay ; and a large proportion of 

 these fragments have been derived from a distance, masses from the 

 Coal-measures being very abundant. The majority of the fragments 

 have their angles only slightly rounded, but are often scored and 

 scratched in all directions. 



In many places in this locality, patches of sand and gravel of 

 considerable area (even from 80 to 90 yards in longitudinal section) 

 occur in this clay ; and it is a noteworthy fact that, as has already 

 been observed, no shells are present in these patches, a strong proof 

 that the fragments of shells which I find in the surrounding clay 

 have been drifted or carried with the other ingredients of the clay, 

 for had they been living in the neighbouring waters during the 

 time the ' Purple ' clay was in process of formation, we might have 

 reasonably expected to find their perfect remains in these inclosed 

 sands, precisely as they are found in the sand-beds in and on the 

 ' Basement ' clay. 



The thickness of the ' Purple ' clay in this neighbourhood is very 

 irregular, and its upper surface is deeply eroded into innumerable 

 hollows, which are often partially filled with a rough heterogeneous 

 gravel, evidently in great part derived from the clay itself, and I 

 agree with Messrs. Wood and Pome in concluding that the mass 

 has suffered extensive denudation. 



Sparsely scattered through this clay from top to bottom are the 

 shelly fragments already referred to as being those which first at- 

 tracted my attention to the subject. They are more water- worn and 

 rounded than those from the lower beds, and rarely, or never, ap- 

 proach perfection, the hinge-line and umbo (the strongest part) being 



