TRANSACTIONS OF SKCTION C. 



731 



f». The Value of drtai It'll Gcolofjli'al Mofm In relation to Watrr-wpply and 

 otiur Fmdical (^ursiimi.i. lUj W. Whitaki'.I!, B.A., F.d.ii. 



Thdso maps oftlio (icoloL'ical Siirvov oC iMifrland in which various divisions of 

 tiic l)i'it't havi' been coloured tell us, as a rule, a very liili'erent tale iVoui tiic corre- 

 spoiiiliii;.'' siieets in which tiio Drift is iiriiored, and it is only tliose Drift maps tliat 

 really jjive us a true idea of tlie nature? of tlie surface. Indeed in many districts a 

 {jeolo^'ical map tliat does not show the Drift is comparatively useless for most 

 practicid purposes, at all events in a populous country like J^noland, where in some 

 capes such a map is even misleading,'-. .Moreover, it is not enough merely to mass 

 Drift as siicli, but its constituent members should be fairly distiniruished, not 

 iiii'Vi'ly witii re<;ard to their classification or relati\e age (and therefore their order 

 of superposition), Init also ns to \\unv composition, whetlier of clay, loam, or 

 (Travel and sand. To illustrate this there were exhibited cojjies of the two versions 

 oF luany of the fieological Survey 3Ia])s of the Ijondon Jiasin, with and without 

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



I. Large tracts, shown as ( 'hulk on one version, really consist, at tlie surface, 

 ni'tlie geuiirally impervious JJoulder < 'lay, whilst over others the Chalk is covered 

 liy Ihickearth ami Clay-with-tlints : all these beds being such as give a character to 

 till' country very different from what we find where tin? Chalk is bare. 



'2. Parts of the wide-spreading area ot'tiu? London Clay (of the Driitlessmaps) are 

 roally ([uite altered, and de]nived of their clayey character, by the sheets, long 

 stri])s, and more isolated patches of gravel and sand that occur so often, ■whether 

 along the river-valleys or over the higher ]ilains. 



.'i. The sandy permeable (Jrags are in great part hidden by Drift, which, though 

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

 widespread is the Glacial Drift in the greater part of Xcn-folk and .Suffolk that 

 only a Drift edition of the (leological Survey Maps of the eastern parts of those 

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

 fiction. 



To illustrate the important bearing- which these Drift mai)9 have on a great 

 question, that of water-su]iply from the (.'balk, the author also exhibited some s])ecial 

 maps, wliich 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. Qi> the Mode of Occurrencr of Precious Stones and Mrlals in India. 



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



For full 0,000 years India has been known as the source of precious stones and 

 metals, but scarcely 200 years have? elapsi'd 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 nuist bo imdertaken, 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 th(!y 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 w^ould 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 



