490 On the Agricultural Geology of England and Wales. 



the chalk ^ — that the calcareous matter was dissolved by the 

 carbonic acid mixed with rain-water, and carried off in the form 

 of supercarbonate of lime ; while the siliceous and argillaceous 

 particles of the chalk, audits flints, remained behind, as on a filter. 

 The rapid changes in the composition of the surface soil from 

 sand to clay, and the intermixture of white calcareous soils with 

 dark-coloured non calcareous soils, furnish a strong argument 

 against this assumption. If it were true, the composition of the 

 substratum of chalk should vary with the varying composition 

 of the soil, which is not the case ; and it is a palpable absurdity 

 to suppose that atmospheric action would have dissolved all the 

 calcareous matter out of a considerable depth of chalk, and yet 

 have left calcareous soils and chalk rubble undissolved. There 

 are, however, positive proofs of aqueous transport in these soils, 

 in the presence of alternating deposits of tough clay and sandy 

 loam, of different colours and tenacity, together with fragmentary 

 chalk, and layers of pebbles derived from the eocene tertiaries, 

 large angular flints being dispersed irregularly through the whole 

 series. The preceding diagram, p. 489, exhibiting a case of this 

 kind, is extracted from a paper recently published in the ' Quar- 

 terly Journal of the Geological Society' — On the Origin of the 

 Soils which cover the Chalk of Kent (vol. vii. p. 35), and for 

 the use of which the Journal Committee are indebted to the 

 kindness of the Geological Society. 



Again we draw attention to the fact that these appearances, 

 which are general in other chalk districts, are found in Kent, in a 

 district in which some geologists consider that there are no traces 

 of marine action more recent than that of the eocene or miocene 

 tertiaries. We have gone into these details respecting the soils 

 upon the chalk, because they prove, by the independent testimony 

 of a number of agricultural observers, the existence of a great 

 variety of soils on a rock of very uniform mineral character, and 

 because they prove those variations to depend not upon the com- 

 position of the rock on which they rest, so much as upon elevation 

 and form of surface. We have collected evidence showing equal 

 variations in the soils on the strata below the chalk, in which the 

 changes are partly due to the superficial deposits, and partly to 

 varying mineral characters in the rock formations. It would 

 require, however, a volume rather than an essay to do justice to the 

 subject. There is, moreover, a deficiency of information suffi- 

 ciently precise to permit the variations of soil to be traced in 

 each case to their respective causes, without a special examina- 

 tion of an extensive district for that purpose. 



Greensand. — The subdivisions of the greensand are usually 

 considered the upper and lower greensand, with the gault inter- 

 posed between them. To these must be added the red chalk of 



