BOULDEE-CLATS OF LINCOLNSHIRE. 129 



east of the Lincolnshire Wolds do not form parallel series. If the 

 Chalky Boulder-clay and the Purple Boulder- clay were correla- 

 tives, we should be confronted with the anomaly of a continuous 

 succession existing on one side of the Wolds, while there is a 

 discontinuous succession on the other. 



Assuming that they are not parallel series, and also supposing 

 for the moment that the brown clays on either side of the dividing 

 ridge in Lincolnshire are complete correlatives, then it is the 

 Chalky Clay which is unrepresented on the eastern side. Now in 

 East Lincolnshire the base cannot be seen ; but in Yorkshire there is 

 a grey and chalky Basement-clay (beneath the Purple-clay) which 

 was originally regarded by Messrs. Wood and Rome as the equivalent 

 of the Upper Glacial-clay of East Anglia. Moreover we have Mr. 

 Lamplugh's testimony as to the appearance of a break with more 

 or less unconformity between this Basement-clay and the overlying 

 Purple-clay. 



I have little hesitation therefore in considering the Basement- 

 clay of Holderness the sole representative of the grey and white 

 Boulder-clays of Lincolnshire, and in regarding the overlying beds 

 of Brown Boulder-clay, with their associated loams, sands, and 

 gravels, as newer and higher members of the great Glacial series. 



This conclusion differs from that recently enunciated* by Mr. 

 Searles Wood, but it is not the only point on which his earlier views 

 appear to me to be sounder that those he has subsequently 

 elaborated. 



The position of the chalky " Basement-clay " at and below the 

 sea-level in Holderness, while on the Wolds of Lincolnshire it rises 

 to a great height above the sea, offers no difficulty to this correlation ; 

 because the same clay occurs at nearly as low a level on the west 

 side of those Wolds. I apprehend, indeed, that the Chalk Wolds were 

 at one time completely mantled by the " Chalky Clay" from side to 

 side ; just as the Jurassic ridge was clearly so covered in Rutland 

 and South Lincolnshire. 



Fig. 4. — Diagram to shoiu the Erosion of the Chalk Wolds, 

 o 



O, older Boulder-clay. N, newer Boulder-clay. 



The available evidence seems to indicate that the eastern slope of 

 the Chalk W^olds was invaded and destroyed by marine erosion 

 during a subsequent submergence, at or immediately before the time 

 when the newer (brown) clays were deposited, and that these were 

 laid down upon the plane of erosion so formed. This idea is 

 expressed in fig. 4, which is not a section along any particular line, 

 but only a diagrammatic representation of the relations above 

 suggested, the plane of erosion being partly across the Basemen t- 

 * Quart. Journ. Geol. Soc. vol. xxxvi. p. 527, and xxxviii. p. 712. 



