Notices of Memoirs — W. WhitaJier's A ddress. 25 



The supply of Norwich, taken from the Wensum, is I believe free 

 from serious contamination. 



In the western part of Norfolk there are large quantities of chalk- 

 water, which may be said to run to waste, and the abstraction of 

 which it seems to me would result in the improvement of certain 

 tracts that are now water-logged. This water flows into streams that 

 are really little else than drains, and not always sufficient ones, for 

 large tracts of lowland, which tracts would also be improved by 

 being rid of some of the water. The parts where the springs rise 

 are often of a peculiar nature, the dissolving away of the chalk having 

 caused the formation of a great number of small hollows, more or 

 less round in shape, from the sinking in of that rock and overlying 

 sand and gravel. The bottoms of these hollows are filled with 

 water, probably because they reach the saturation-level of the Chalk, 

 the same cause that gives us the much larger sheets of water in the 

 District of the Meres at a higher geological level in the Chalk, the 

 tracts now alluded to being near the base of the formation. 



At our last Yearly Meeting I remarked that the completion of the 

 Geological Survey of a district did not result in the exhaustion of 

 that distinct, as regards geological investigation, but rather that our 

 work aided future workers. The set of maps to which I have now 

 to call your attention is an illustration of this ; for, whilst they can 

 only be made after a detailed survey, yet they need for their con- 

 struction sometliing more than is shown on any Geological Survey 

 Map, or that can be easily worked out from a Memoir, They need 

 a consideration of various local circumstances, which it is open to any 

 careful geological observer to make : there is indeed only one thing 

 in which they absolutely follow the geological maps, that is, as regards 

 the area of bare Chalk. 



I would remark at once that these maps are not geological maps, 

 and it is important that you should remember this, or you will mis- 

 understand them, though they are founded on geological maps : 

 their object is to show what comes between the Chalk and the rain. 



For this purpose it was found that all our geological divisions, 

 from the Chalk upwards, could be grouped under 4 heads, as 

 follows : — 



1. Areas where the Chalk is bare (except of course for soil), and 

 in which therefore water has free access to it. 



2. Areas where the Chalk is covered by permeable beds only, or 

 by beds almost wholly permeable, and in which therefore water has 

 nearly free access to it, 



3. Areas where the Chalk is covered by beds of varying character 

 or mixed structure, partly permeable, partly impermeable, and in 

 which therefore water has but a limited power of access to it. 



4. Areas where the Chalk is protected by impermeable beds, and 

 in which therefore water does not sink into it. 



Now, in colouring these maps in accordance with the above 

 scheme, and in thinking over the colouring of others not yet to hand, 



