TRANSACTIONS OF SECTION C. 731 



9. The Value of detailed Geological Maps in relation to Water-supply and 

 other Practical Questions. By W. Whitakee, B.A., F.G.ti. 



Those maps of the Geological Survey of England in -which various divisions of 

 the Drift have been coloured^ tell us, as* a rule, a very different tale from the corre- 

 sponding sheets in which the Drift is ignored, and it is only these Drift maps that 

 really give us a true idea of the nature of the surface. Indeed in many districts a 

 geological map that does not show the Drift is comparatively useless for most 

 practical purposes, at all events in a populous country like England, where in some 

 cases such a map is even misleading. Moreover, it is not enough merely to mass 

 Drift as such, but its constituent members should be fairly distinguished, not 

 merely with regard to their classification or relative age (and therefore their order 

 of superposition), but also as to their composition, whether of clay, loam, or 

 gravel and sand. To illustrate this there were exhibited copies of the two versions 

 of many of the Geological Survey Maps of the London Basin, with and without 

 Drift, from which the following important points could be at once seen : — 



1. Large tracts, shown as Chalk on one version, really consist, at the surface, 

 of the generally impervious Boulder flay, whilst over others the Chalk is covered 

 by Brickearth and (Jlay-with-flints ; all these beds being such as give a character to 

 the country very different from what we find where the Chalk is bare. 



2. Parts of the wide-spreading area of the London Clay (of the Driftless maps) are 

 really quite altered, and deprived of their clayey character, by the sheets, long 

 strips, and more isolated patches of gravel and sand that occur so often, whether 

 along the river-valleys or over the higher plains. 



3. The sandy permeable Crags are in great part hidden by Drift, which, though 

 often consisting of sand and gravel, is sometimes of Boulder Clay. Indeed so 

 widespread is the Glacial Drift in the greater part of Norfolk and Suffolk that 

 only a Drift edition of the Geological Survey Maps of the eastern parts of those 

 counties has been issued ; a map without Drift would necessarily be a work of 

 fiction. 



To illustrate the important bearing which these Drift maps have on a great 

 question, that of water-supply from the Chalk, the author also exhibited some special 

 maps, which he has made to show the areas over which rain-water has access to 

 the Chalk, as distinguished from those over which the surface-water cannot sink 

 down into the Chalk, or can only do so very partially. These maps were more 

 particularly noticed in Section G. 



10. On the Mode of Occurrence of Precious Stones and Metals in India. 

 By V. Ball, M.A., F.B.S. 



For full 3,000 years India has been known as the source of precious stones and 

 metals, but scarcely 200 years have elapsed since other countries yielding precious 

 stones have entered into competition with her ; and it is only within the present 

 century that she has ceased to hold a pre-eminent position as a supplier of the 

 markets of the world. 



In order to arrive at a full and satisfactory elucidation of this subject, two 

 branches of inquiry must be undertaken, one based upon what has been actually 

 ascertained by careful geological exploration of the country, and the other upon 

 such historical records as are available of the former production of the minerals 

 in question, and of the indications of the sites where they were mined. 



By means of our present knowledge of the geology, it has become possible to 

 give definite form to many vague statements by early writers, and to recognise the 

 actual positions of mines which are now, by the people of the localities themselves, 

 forgotten and deserted. In the majority of these cases, had the geologist not got 

 the historical hand to guide him he would be unwilling to predicate the presence 

 of such minerals from mere superficial examination. 



As a collateral result, many of the widespread myths and fables connected 

 with mining have proved to have originated in peculiar local customs. They 



