BOFLDER- CLAYS OF LINCOLNSHIRE. 123 



brown Boulder-clays has in most places been destroyed by post- 

 glacial detrition. The only other locality known to me where 

 beach-deposits contemporaneous with the upper portion of the 

 brown clay occur is near Kirmington, in sheet 86. These have 

 been mapped and investigated by Mr. C. Eeid, and will be described 

 by him in the explanation of that sheet. They are interesting as 

 containing a large marine fauna. 



There is also another point of interest in connection with the dis- 

 tribution of the brown clay round the Fen borders. In 1879 I 

 drew attention to the peculiar way in which the newer Boulder- 

 clays (then supposed to be Ilessle Clay only) terminated southwards 

 in East Lincolnshire *. Leaving the Fen border at Stickford, the 

 brown clay is prolonged, southwards in a long ridge or bank by 

 Stickney and Sibsey for a distance of seven miles ; and while the 

 Pens on the east side of this bank are underlain by the same 

 Boulder-clay, those on the west side rest directly on Kimmeridge 

 Clay or on the older Boulder-clay which comes in further west. 



This struck me at the time as a fact which was both remarkable 

 and difficult of explanation ; for if the contours of this part of 

 Lincolnshire during the formation of the newer Boulder-clay were 

 anything like what they are now, it is hard to conceive any valid 

 reason why this clay should be so peculiarly and partially distri- 

 buted ; why it does not continue to form a bordering plateau west- 

 ward from Stickford, as it does to the eastward of that place and 

 along the east side of the Chalk Wolds. 



Not only is the newer Boulder-clay absent from Stickford to Tat- 

 tershall, but no sign of it has ever been discovered along the eastern 

 side of the Witham level from Tattershall to Lincoln, although in 

 the present paper I have described a continuous strip of this clay as 

 bordering the western side of this level from Billinghay to and 

 beyond Hanworth Booths. 



I think we may infer from these facts that the contours of the 

 whole district lying to the east of the Witham level, and along the 

 Fen border as far as Hagnaby beck, have been greatly altered in 

 post-glacial times, that is, since the formation of the newer Boulder- 

 clay. The widespread deposits of gravel and sand of the lower 

 parts of the tract in question demonstrate that it has suffered 

 great erosion and detrition in post-glacial times ; so that altogether 

 it seems probable that, at the time when the newer Boulder-clay 

 was formed, this tract was occupied by a mass of the older Boulder- 

 clay, rising above the level at which the newer clay was laid down 

 in the Fen district, and forming a promontory which jutted south- 

 wards over what is now termed the West Fen. 



On this supposition the existence of the curious ridge of Boulder- 

 clay running through Stickney and Sibsey finds a natural explana- 

 tion ; for if there was originally higher ground to the west of this 

 ridge, it may be regarded simply as a continuation of the bank 

 formed against the old shore-line below Toynton and Keal (see 



* See Quart. Journ. Geol. Soc. vol. xxxv. p. 397. 



