W. W/iitaker — On Geology and Consumption. 501 



formations of the three counties, and the description of the strati- 

 graphical conditions and physical features of the 58 districts which 

 supplied the statistical data ; and, in the second place, being directed 

 to an estimation of the number of people living on each formation. 

 In the former of these the knowledge of my colleague, Mr. Topley, 

 was made use of for part of the Wealden area ; whilst Mr. Bristow 

 gave some information on the southern edge of Sussex and Hamp- 

 shire, a very small part of which latter county came within the 

 bounds of Dr. Buchanan's work. 



The geological formations of the South-East of England range 

 from the Bagshot Beds down to the Hastings Beds, without any 

 gap, the series being perfect. Besides these there are alluvial flats, 

 both as broad marsh-lands and as narrow strips along streams ; 

 fringes of shingle and blown sand along parts of the coast : and a 

 great number of tracts of Drift loam, gravel, and sand on all forma- 

 tions, at many levels, and of various sizes. 



In working out conclusions from the data that had been got 

 together it is clear that, as saturation of subsoil was the chief thing 

 to be considered, the mere permeability or impermeability of a 

 formation was not the only condition to be examined ; but that the 

 height and slope of the ground and the dip of the beds were im- 

 portant matters, as well as any other fact that bore on the water- 

 holding power of the beds or their capacity for drainage in any 

 district. 



From the varying character of some of the formations (as for 

 instance the Lower London Tertiaries, the Lower Greensand, and 

 the Hastings Beds), great care had to be taken to avoid hasty 

 generalisations, and a detailed consideration of each particular dis- 

 trict was made needful, the same formation having different characters, 

 and giving rise to dilferent physical features and conditions in dif- 

 ferent parts. 



Again, though a formation, as the London Clay, might be of the 

 same character throughout the whole area, yet any generalisation at 

 once founded on that fact might have been false ; for it was soon 

 found to be absolutely essential to consider how the countiy formed 

 by such a homogeneous formation is modified by the occurrence of 

 cappings of gravel, &c., districts of bare clay being practically quite 

 distinct from those where the clay is covered by 10 or 20 feet of 

 pervious gravel. 



This detailed method of examination sometimes showed that large 

 areas formed of like beds, and which at first sight might have been 

 thought to be of like character, were really far from being so : thus 

 the London Clay and the Weald Clay are both thick masses of im- 

 permeable beds of much the same comjDositiou, but the broad tracts 

 over which they crop out are for the most part quite unlike. The 

 difierences between the two great clay-couutries of the South-East 

 of England are so many that perhaps they may be best sho^vn 

 when thrown into the form of a table, as below, from which it may 

 be seen that, whereas the London Clay is so disposed as for the 

 most part to allow of the flowing ofi" of surface-water, the Weald 



