Chiscldan to CoUincjboiirne. 101 



and so when these beds are found the lower chalk might yield a 

 good deal of water. 



But neither this division nor that of the middle chalk can he 

 compared ^\^[th the upper chalk for purposes of water supply. The 

 many layers of flint and the fissiu-es so plentiful in this formation 

 assist percolation, and the water sinks through the chalk till the 

 level of satm-ation is reached. This level rises and falls with the 

 amount of rainfall. 



Agriciiltiu'ally the upper chalk is very important, forming a good 

 arable soil, especially when covercid by the red clayey flinty soil 

 known as the clay-^vith-flints, and only foimd on the upper chalk 

 in tliis district. The carbonated rain water, the carbonic acid 

 being derived fit'om decaying vegetable matter, percolating through 

 the flinty chalk, removes the carbonate of lime and leaves the 

 clayey part of the chalk as a red clay stained by ii'on. 



Thus, from an agricultural point of view, the lower chalk forms 

 the heavy arable land, the middle chalk the down land, and the 

 upper challv, when bare, the light arable land. 



The clay-with-flints and the Tertiary debris often fill pipes 

 many feet deep. Mr. Codrington, in his paper on the Greology 

 of the Berks and Hants Extension and Marlborough Railways, 

 describes some pipes 30ft. in depth in the cutting between Savemake 

 and Marlborough, near Wemham Farm. 



Mixed "with the clay-with-flints is to be found a good deal of 

 mottled clay, the remains of the Tertiary beds. 



In the brickj'ard on the top of Salisbury Hill, near the Marl- 

 borough Water Works reservoir, are some very good sections of 

 both these clays. The pipes are Hned with a thin coating of clay- 

 with fliiits and filled "with a considerable thickness of Tertiary 

 clays, the debris of the Tertiary beds. 



It is this clay-with-fliuts and the existing outliers of the Tertiary 

 beds, forming a soil so favom-able to the growth of trees, to which 

 Savemake Forest owes its existence. The forest area roughly 

 marks out the clay area, and though to the west of the forest there 

 is a considerable clay area bare of trees, this is because they have 

 been cut down. The forest must once have extended as far 



