J. E. Marr— Glacial Deposits. 269 



escape such contortion, unless they were themselves consolidated, 

 and their nature is such that they can have been consolidated only 

 by being frozen, which could not occur over large areas at the 

 bottom of the muddy sea, in which according to this view the ice- 

 bergs were drifted. 



The conformation of the ground around Sudbury is of such a 

 nature that it is extremely difficult to account for the stranding of 

 icebergs in some of the spots where the contorted drifts occur, as, for 

 instance, at the bottom of the Stour valley. 



We come now to the last suggested cause of the production of 

 contortion, viz. by the passage of land-ice. This agency is con- 

 sidered by Mr. Searles V. Wood, jun. (Q J.G-.S. vol. xxxvi. p. 479), 

 to have produced the Chalkj'- Boulder-clay with which the so-called 

 Upper Boulder-clay of this district is identified. The map No. 4 of 

 Mr. Wood (Q.J.G.S. vol. xxxviii. plate xxvi.) shows the ice which 

 produced this clay blocked by the British ice to the north, and 

 spreading over East Anglia parallel with the southern trend of this 

 clay, i.e. in a general east and west direction. Could not such a mass 

 of ice produce all the phenomena which are observable in the Sudbury 

 area? The difficulty of accounting for the undisturbed state of the 

 Tertiary rocks disappears at once upon this view. If the area over 

 which the ice passed was a land-surface, it would be frozen so hard 

 that the now incoherent rocks would be solid, and would be treated 

 in a similar way to the harder rocks of other districts. Such seems 

 to be the case. We find a series of ridges having a general E. — W. 

 trend, composed of Crag sands, with intervening depressions some- 

 times cut deeply into the Chalk, as in the case already referred to, 

 and figured by Mr. Whitaker. These ridges would be veritable 

 rocJies moiitonnees, whicli accords well with the appearance presented 

 by that on Balingdon Hill. The fragments torn off and included in 

 the drifts, being frozen, would not be crushed, but retain their form 

 of large and small subangular boulders, such as that seen in Mr. 

 Green's pit. Only on this view is the regular bedding of the torn 

 Tertiary beds comprehensible. 



Next, the contortion of the drifts, the relationship of the folds 

 to the inequalities below, the large quantities of local material which 

 enters into their composition, and the absence of marine organisms, 

 is satisfactorily explained upon this supposition. I have already 

 referred to the similarity of the divisional planes to those of the 

 fluxion -structure of igneous rocks, which is not to be confused with 

 the fluxion -structure described by Mr. Hugh Miller (Eep. Brit. Assoc. 

 1884, p. 720) as occurring in Till. Moreover, the great overfolds 

 in the drift, as above remarked, seem to require the occurrence of 

 considerable lateral pressure to produce them. That lateral pressure 

 does produce a similar structure in the stratified deposits of land-ice 

 is apparently indicated by the case figured in the " Meddelelser om 

 Gronland," part iv. pi. iii., where a glacier ending in a narrow valley 

 has its stratified sand and clay thus overfolded where the ice has 

 been compressed against the sides of the valley. That this sand and 

 clay may be interstratified with Boulder-clay produced by the same 



