Yol. 68.] GLACIAL SECTIONS ROUJSTD SUDBURY. 25 



II. Sands and Silts. 



Since the date of publication of the Survey Memoirs additional 

 aids have been furnished in the Ordnance Maps, by their larger 

 scale, and by their contour-lines. 



Six of the above-named pits lie on or near the 200-foot contour. 

 In the two pits on Gallows Hill (3), and in the adjacent iuner 

 Alexandra Pit (6), is exposed a thick series of finely-bedded sandy 

 silts, of which more than 30 feet can be seen. About half a mile 

 east, at the same level, in the sand-pit on the IN'ewton Road (7), 

 is an exposure of at least 20 feet of bedded sands — chiefly pure 

 sand, but in two or three beds a little clay is present. 



Across the river, at the same level, in the sand-pit on Ballingdon 

 Hill (13), are nearly 40 feet of somewhat current-bedded, stoneless 

 sands, similar to the last, except that clayey sand occurs only at 

 the top. Sands of similar character seem to occur not far off, in 

 the parish of Middleton. In all these pits, except that on the 

 Newton E,oad (7), Boulder Ciaj overlies the beds. 



The sand-pit north of Great Cornard Church (10), east of the 

 rifle-butt, is just below the 200-foot contour. It is in red sands, 

 which are, I think, a remnant of Crag. Similar red sands can be 

 traced at short intervals up to the pit (2) in which Mr.W.Whitaker 

 recognized Crag. 



There seems, then, to have been at Sudbury an extensive deposit 

 of sediments, sands, and silts, reaching nearly up to 200 feet above 

 Ordnance datum. They are all somewhat current-bedded. Do 

 they not indicate deposition in water which was shallow, and 

 affected by only moderate currents ? This level of 200 feet O.D. is 

 120 feet above the alluvial meadows at the bottom of the valley. 



III. BouLDEE Clay. 



In the Gallows -Hill (3) and inner Alexandra (6) Pits, upon 

 the bedded silts lies Boulder Clay. This forms a sheet which is 

 exposed continuously for several hundred yards. The ground 

 behind the pits rises gradually into the plateau of Boulder Clay, 

 which attains an altitude of nearly 300 feet O.D., and covers 

 several square miles. The clay is found in wells to have a thick- 

 ness of sometimes over 100 feet. We may deduce that these 

 sections show a true base of the clay. 



Its junction with the silts can be scrutinized, touched, tested. 

 The passage from silts into clay is seen to be continuous : there is 

 no sudden break. There are coarser beds in the upper foot or so 

 of the silts, finer bands in the lowest foot of the cl^y. Flints are 

 not abundant in the lowest part of the clay ; where they cease to 

 occur, the bed can hardly be assigned definitely to either division. 

 The chalk-pebbles in the clay are rounded : smaller rounded chalk- 

 pebbles are found at several horizons in the silts. It seems that 

 the process which produced the silts changed by a gradual transition 

 into the process which produced the Boulder Clay. 



It may be mentioned that bedded silts are also seen lying under 



