/. E. Marr — Glacial Deposits^ 267 



The Upper Boulder-clay is lighter than the Lower, but otherwise 

 altogether like it ; but it contains thin seams of gravel and loam. 

 A large number of boulders were lying in the pit, probably from 

 both clay and gravel, and consisting of various schists, granites, 

 fragments of basaltic columns, limestones, sandstones, etc. 



The sands, gravels, and loams in this pit are, as in the case of 

 those on the left bank of the Stour, very extensively contorted. 



So much for the facts. It remains to be considered what light, if 

 any, they throw upon the origin of these particular drifts. That we 

 do want some light is evident, when we find some writers assigning 

 a marine origin to the East Anglian drifts, others a terrestrial one, 

 whilst Mr. Searles Wood, jun., in his last communication concerning 

 these drifts (Q.J.G.S. vol. xxxvi. p. 457), calls into play the agency 

 of both land-ice and the sea. I wish it to be understood that the 

 following remarks apply only to the actual Sudbury sections. 



The great difficulty connected with the above-described sections is 

 the occurrence of intensely-contorted drifts upon an irregular surface 

 of absolutely undistiu'bed Tertiary beds, which are now, with one 

 exception (the top of the Crag pebble bed), in a soft and incoherent 

 state. Two questions suggest themselves : 



1. Were the contortions produced in the area in which the 

 contorted beds now lie, or were the contorted deposits borne from a^ 

 distance ? 



2. If the former, why are not the incoherent beds, on which these 

 contorted deposits rest, themselves disturbed ? 



In answer to the first question, it may be confidently stated that 

 the contortions were produced in the beds in the area in which they 

 now lie, firstly, because the contortions adapt themselves to the 

 irregularities of the surface on which the contorted beds rest, as 

 seen in the case of the Crag ridge in Mr. Green's pit, and of a section 

 figured by Mr. Whitaker as occurring on the east side of a chalk-pit 

 about half a mile east of St. Peter's Church (Geol. of N.W. Essex, 

 etc.), where the drifts are looped into a hollow in the Chalk; 

 secondly, because the contorted deposits have been largely derived 

 from the local rocks. Thus we find many fragments of Crag, large and 

 small, in the gravel north of the Crag ridge in Mr. Green's pit, and 

 fragments of the green Thanet Sand scarcely even re-made in the- 

 patch of Boulder-clay in the northern part of that pit just where 

 the green Thanet Sand has been scooped out. Similarly, at the top of 

 Balingdon Hill, the base of the Boulder-clay contains much Crag 

 material. Again, Mr. Whitaker describes the passage of re-made 

 green Thanet Sand into the actual deposit, so that the line of junction 

 is not to be ascertained. Mr. Penning, in the same Memoir, p. 59, 

 remarks that "the main substance of the [Boulder-] clay indeed 

 consists of material received from rocks at no great distance from 

 the point where it may be observed," and Mr. Dalton adds that 

 " some parts of the Boulder-clay consist almost entirely of chalk. 

 Where it lies directly upon the London Clay, it is often mainly 

 composed of the latter, being a blackish or reddish-brown clay with 

 a few pieces of chalk or other rocks." It is clear then that the 



