XX111. 



rocks, and fragments of basalt, quartz, granite and other igneous rocks.. 

 There is nowhere any approach to stratification, except in a few places 

 at the extreme base of the deposit, which also has here and there irre- 

 gular beds intercalated of gravel and brick earth. This deposit appears 

 to be the moraine profonde of a great ice sheet, which covered the whole 

 country as in Greenland, and which has left its debris in the place over 

 which it once extended. The period, during which this deposit was laid 

 down, was the most extreme of the Glacial Epoch, and it was followed 

 by successive changes of warm interglacial periods and two other periods 

 of glaciation ; but at neither of these times did land ice extend as far 

 South as Suffolk, and it has therefore left no trace in this County. The 

 Great Chalky Boulder Clay is well -developed in both divisions of the- 

 County, and good sections are to be seen at Haughley and Thurston, 

 and in the neighbourhood of Bury at Honington and Ixworth Thorpe. 

 Economically it is used as a dressing for light lands, and, mixed with 

 straw, is made into blocks, which baked in the sun, are used for roughi 

 building purposes. 



The Post glacial beds consist of beds of plateau and river gravels. 

 It will be noticed, on studying the drift sections further North, that the- 

 beds of interglacial or warmer epochs are chiefly gravel, derived from 

 boulders and stones contained in the clays. They were probably formed 

 in the following manner : When warm weather began, ice would melt, 

 rapidly, all the stieams would be filled, and great floods would occur 

 every year and overwhelm the country, washing out the stony consti- 

 tuents of the moraine deposit, and relaying them as beds of gravel. 

 Intermorainic lakes would form, whose barriers suddenly giving way,. 

 would cause destructive floods. These beds are developed near Bran- 

 don, Santon Downham, Mildenhall, and the valley of the Lark, and are 

 of great interest as containing relics of Palaeolithic man. 



The stones comprising these beds are not rounded like water-worn 

 pebbles, but are angular, though somewhat blunted, so little have they 

 been rolled that I have obtained several very beautiful flint casts of 

 echinoderms and other fossils. In a few localities only is there evidence.- 

 of regular stratification. 



