TRIMMER ON SAND-GALLS IN THE NORFOLK CHALK. 



305 



lines of section, the furrows are excavated in solid chalk, and 

 they are separated from one another by an intervening ridge of 

 solid undisturbed chalk. 



Fig. 3. Thorpe Chalk Pit. 



( Cross Section of the bottom of the furrow G M. ) 



W. E. 



1. 



Solid chalk. 



0. 



Yellow ochre. 



s. 



Sand. 



c. 



Chalk. 



u. 



Sand mixed with umber. 



3. 



Layer of reconstructed chalk 



On the line of section n o, each of the furrows is from 7 to 8 

 feet deep, and, at the surface of the solid chalk, is about 4 feet 

 wide ; but on the line of section a g, both the furrows are wider 

 and shallower. At and near the line of section n o, the width of 

 the furrows on a level with the surface of the solid chalk, is some- 

 times less than it is about a foot and a half below that level ; but 

 at a greater depth the width again diminishes, and it then tapers 

 downwards to the bottom. Sometimes, however, the transverse 

 section is nearly that of a wedge. 



Near the line of section n o, the lower part of the furrow G m, 

 to the height of about a foot from the bottom, was irregular in 

 shape, and, at that height, was from 1^ to 2 feet wide. This part 

 was sometimes filled with a mixture of yellow ochre and umber, of 

 a blackish or brown colour, and very low specific gravity : some- 

 times the umber lay above and the ochre below, a thin layer of 

 fine sand separating the two ; sometimes a layer of fine ferruginous 

 sand lay beneath the ochre and umber, and sometimes, as in Fig. 

 3., thin irregular layers of chalk were mixed with the other 

 contents of this lower part of the furrow. At the bottom of the 

 furrow A B, near the point A in the ground plan, was an accumu- 

 lation of water-worn pebbles, which was covered by sand. (See 

 Fig. 4.) 



VOL. I. X 



