118 



A. J. JTJKES-BEOWNE ON THE 



and for details of the sections visible in tlds neighbourhood, I may 

 refer to my paper "On the Southerly Extension of the Hessle 

 Boulder-Clay in Lincolnshire "*. The map accompanying that paper 

 also shows the manner in which this clay, together with the under- 

 lying Purple Clay, stretches northward, and forms a broad tract of 

 undulating land between the Chalk Wolds and the eastern marshes. 

 That map, however, having been drawn before the boundaries of the 

 Boulder-clay had been accurately mapped north of Alford, it is 

 necessary to give some account of its inland boundary from this 

 point, and the map (p. 115) will enable the reader to follow the 

 ensuing description. 



This boundary, to the west of Alford, is almost a straight line ; 

 the clay ends abruptly against the rise of the Chalk Wolds, and the 

 depth of the clay increases with the rise of the ground from Alford 

 towards the hills. Thus near Alford the usual depth of the Boulder- 

 clay is about sixty feet, but near Rigsby a well was sunk within a 

 furlong of the boundary-line, and passed through ninety feet of clay 

 without piercing it. These facts show that the plain of Chalk on 

 which the Boulder-clay rests is nearly horizontal, and extends up to 

 the foot of the Wolds. They also seem to indicate that the clays 

 are banked up against a buried cliff of chalk. This sb \rp boundary- 

 line continues north-westward for about two miles, till it is broken 

 by the outlet of the Calceby beck between Aby and Belleau. Here 

 there is an extensive bed of gravel, intercalated apparently between 

 an Upper and Lower Boulder -clay, and evidently a beach-formation, 

 containing broken marine shells in the sandy beds, and rolled 

 pebbles of chalk, pierced by Pholades,m the gravel beds. At South 

 Thoresby there are two beds of gravel, separated by a layer of cla}^, 

 about 20 feet thick, and the same is the case at Claythorpe station. 



At and beyond Belleau the Boulder-clay overrides the cliff' or slope 

 of the Chalk, and for some distance caps the ridge which runs 

 through Burwell Park. Prom this place to the neighbourhood of 

 Louth, the boundary is very irregular, outliers of Boulder-clay 

 occurring on the highest hills, and tongues of the same clay 

 occupying the bottoms of the valleys which ramify through the 

 Wolds. The height to which the Boulder-clay here ascends must be 

 nearly 300 feet ; but in colour and general appearance it is precisely 

 the same as that found near the surface of the lower ground. 



I^orth of Louth, for a short distance, the border of the Chalk 

 Wolds is similarly smothered in Boulder-clay ; but near Potherby 

 the boundary descends to a lower level and becomes again sharp and 

 clear. Striking N.N. W., and only interrupted by tongues thrust up the 

 older valleys, it passes into sheet 86, between Wyham and Hawerby. 

 At the latter place the boundary-line appears to pass between the 

 church and " the Hall" occupied by Mr. Harness ; this gentleman in- 

 formed me that a well had been sunk in his yard to a depth of 156 

 feet without meeting anything else than clay. As chalk comes to the 

 surface at a distance of about 150 yards, there is a very steep slope 



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



