/ 



41 



the chalk -marl. Upon this deposit along the base of the 

 north and south Downs, and elsewhere on the flanks of the 

 chalk hills, and in the valleys at their foot, there frequently 

 occurs a superficial layer of earthy or chalky material, 

 which, on careful manipulation, yields quantities of the 

 forarainifera of the chalk-marl in great plenty and variety. 

 Such a storehouse of the remains of the cretaceous microzoa 

 occurs at Charing, between Ashford and Maidstone, at the . 

 foot of the Xorth Downs. It was first observed by me, and 

 I have for many years collected its interesting contents, 

 specimens of which are contained in the slides in the long 

 boxes before you. Athin narrowband of this whiteisb, sandy, 

 enacious, and calcareous clay is traceable for some miles 

 east and west of Charing, widening out occasionally ia 

 the basins or little valleys of the district. This superficial 

 clay, or " chalk-detritus," appears to bave mainly resulted 

 from the action of water on the decomposing surface of the 

 chalk-marl, the outcrop of which, together with that of the 

 upper greensand (here exceedingly thin), is more or less 

 covered by it. At some places flints from the chalk, and 

 even gravel-flints, are found in the detritus, mixed with 

 it at a comparatively modern period ; and, where streams or 

 marshes have had much influence on this detrital bed, fresh- 

 water and land shells of existing species, seed-vessels, and 

 small bones are found in it. This debris is largely made up 

 of the sheUs of numerous kinds of foraminifera, spines of 

 sponges, valves of cytherinaj, fragments of bryozoa, and 

 other minute animal remains. 



THE CHALK. 



The chalk rock and marl have been formed above the 

 upper green sand, and must therefore be of later date. The 

 pure white chalk is composed of lime and carbonic acid, 

 and is a mere aggregation of fragments of shells and other 

 creatures, so minute that upwards of a million are con- 

 tained in a cubic inch of chalk ; the other particles appear 

 to be the detritus of similar structures. These organisms 

 for the moat part are the calcareous chambered shells of 

 the aDimalcules termed foraminifera, all of which belonged 



