GLACIAL BEDS. 



Sii 



been derived from it. Mr. Fisher has observed that the subjacent stratum, where 

 it is of a soft nature, is often worn into furrows and hollows, distinct from the 

 ' pipes ' which are confined to soluble beds. The materials which fill these 

 furrows he calls 'trail,' and it is noticeable that where pebbles occur, their axes, 

 more frequently than not, deviate from the horizontal position. This feature arose, 

 in his opinion, from the pebbles sinking through a muddy deposit, for the effect of 

 friction would be to place them on end, whde the same result would probably 

 take place from the action of frost and thaw on loamy soils containing pebbles. 

 Nevertheless, in some instances, according to Darwin, the vertical position of 

 stones is caused by earthworms. 



Mr. Fisher remarks that the contents of these furrows have contributed to form 

 the warp, and thus we see why the surface-soil sometimes varies so remarkably 



Fig. 91. — Section of Upper Beds at Uphall Brickfield, Ilford, Essex. 



(Rev. O. Fisher.) 

 Thickness of beds shown about 8 feet. 



.* o .' 



t a n (» o 13 



■ Trail. 



5. Warp. 



4. Clayey gravel. 



3. Re-deposited London Clay, with pebbles. 



2. Light-coloured yellowish sand (belonging to the Brick earth series), disturbed by the 



deposition of the Trail. 

 I. Pebbly band in which a tooth of Elephas antiqmis was found. 



over limited areas. The furrows are the tool-marks of the last agent which 

 moulded the surface of the country ; ^ and they are in many places sufo-estive 

 of the action of ice, especially as the beds are not uncommonly dragged up or 

 contorted. In fact in most instances the "furrows" appear to be due to con- 

 tortion, and the gravelly beds that fill them are simply remnants of gravel that 

 perhaps formerly occurred in some thickness. In some cases the contortions may 

 be due to flexures produced by roots of trees, the melting of included fragments of 

 ice (see p. 513), and to dissolution of the calcareous stones.^ 



These contorted surface-beds are of frequent occurrence in the Thames Valley 

 deposits, and good instances are to be seen at Ilford (see Fig. 91), and also at 

 Grays. They occur also at Culham near Oxford, between Walton and 



1 Q. J. xxii. 553 ; G. Mag. 1867, p. 193. 



"^ See Bonney, Cambridgeshire Geology, p. 53. 



