BOTJLDEE-CLAYS OF LINCOLNSIIIRE. 117 



continuous on the eastern flank and soon begins to set in on the 

 western flank. 



The great sheet which slopes northward through Cambridgeshire 

 and caps the islands of Ely and March dips beneath the Fen-level 

 along a line running south of Crowland and Wisbech and continues 

 to underlie the plain of the Fenland by Spalding, Donington, 

 and Boston. It may have been, and probably was, connected 

 with that which spreads over the high laud in the south part of 

 sheet 70, but it is now disconnected by erosion along the Fen 

 border. Unlike the high-level mass, it does not terminate in 

 the latitude of Ancaster, but appears to run northward below the 

 Fens bordering the Witham, emerging along their eastern border by 

 Tattershall, Kirkstead, and Bardney. Thence this Chalky Boulder- 

 clay spreads northward through Wragby and Market Rasen to 

 Brigg, and eastward to Horncastle and the high ground between the 

 valleys of the Bain and the Steeping in sheet 84. 



It also sends a tongue-like prolongation north-eastwards, from 

 Hainton and South Willingham, across the escarpments of the Lower 

 Neocomian and the Chalk, by Gayton-le-Wold and Brough-on-Bain, 

 up on to the summit of the Chalk Wolds near Kelstern and Elkington 

 to the north-west of Louth. Near Gayton the Boulder-clay and 

 associated gravels are seen to be bedded against the slope of the 

 Chalk escarpment, showing that this escarpment had retired to its 

 present position in pre-glacial times. The height of the ground 

 near Kelstern is about 400 feet above datum-level. 



Another important point in connection with the distribution of 

 this Boulder-clay is this, that with the exception of the tongue above 

 mentioned and a small outlying patch to the southward, it is not 

 found anywhere along the broad tract of the Chalk Wolds from 

 their commencement near Candlesby to their intersection by the 

 Humber. This is the more remarkable because this clay caps the 

 high ground formed by the Lower JN'eocomian escarpment near 

 Greetham,Fulletby, and Scamblesby, which is as high as, if not higher 

 than, the corresponding part of the Chalk escarpment. Still the 

 occurrence of the single outlier near Maidenwell, and the fact of its 

 climbing on to the Wolds by Kelstern, seem to indicate that the 

 Boulder-clay once had a continuous extension over these hills. We 

 are consequently obliged to conclude either that the W^old hills 

 have been in some way exposed to more severe and long-continued 

 detrition than the rest of the county, including the Neocomian ridge, 

 or else that the amount of Boulder-clay originally deposited on the 

 Chalk hills was very much less than elsewhere. It is very probable 

 that its thickness was less on these hills, and I have shown in pre- 

 vious papers that erosive agencies have been very active over this 

 tract. 



§ 2. The Range of Brown Boulder- Clays. 



The Eastern Border. — In describing these clays and their mode 

 of occurrence it will be convenient to commence on the north border 

 of the Fenland, near Firsby, a station on the Great Northern line ; 



