618 KE?OKT— 1881. 



cussed were :- — a. Colours and signs for Geological Maps ; h. Nomenclature of rocks 

 and formations; c. Nomenclature of species. This paper was concerned only with 

 the first of these questions, and especially with the resolutions passed by the 

 English Map-Committee, of which Prof, Hamsay is President, and the author 

 Secretary. 



At present, all countries, and many map-makers in each country, have different 

 systems of colouring maps, and it is necessary carefully to study the Index, or scale 

 of colours used, before the maps can be at all understood. The Congress proposes 

 to frame a scheme of colouring which can be used, and readily understood, by all 

 nations. It may not be possible, at least for some time to come, to apply this 

 scheme to national surveys in progress ; but it is to be hoped that the scheme 

 to be adopted will be used in new maps. One important point which the Congress 

 proposes is the preparation and publication of a general map or atlas of Europe, 

 compiled (under the authority of the Congress) from various national surveys, and 

 the work of independent observers. 



The scheme of colouring proposed by the English Committee is one based on 

 the order of colours in the solar spectrum, violet denoting the oMer rocks. 

 Bright reds are reserved for igneous rocks. Me tamorphic rocks will be shown by 

 dark bands of colour over the colour denoting the age; to these will be added 

 bands of colour showing the period at which metamorphism has taken place, 

 when such fact is clearly established ; thus, Silurian rocks metamorphosed in 

 Cretaceous times would be shown by violet, striped with alternate lines of dark 

 violet and green. The sub-divisions of a formation will be shown by shades 

 of the body colour, the darkest shade denoting the oldest sub-division. The 

 letter denoting the formation will be the capital initial letter of the name of the 

 formation. With very small accommodations one system of lettering can be made 

 to apply to all countries. 



It has been found impossible to adhere strictly to the order of colours of the 

 spectrum, and an interpolation has been made of browns and greys for the series 

 of beds between the Silurian and the Lias. 



Examples of maps and tables of strata were exhibited, coloured according to 

 the plan adopted. Also a series of indexes of colours issued at various dates by 

 the Geological Survey, commencing with one, in MS., by Sir II. Ue la Beche, 

 the founder and tirst Director-General of the Survey; this was made in 1882. The 

 author also drew attention to a proposal, made by Mr. J. W. Salter, before this 

 Association in 1847,' and again in a map exhibited at the International Exhibition 

 in London, in 1862, to colour Geological maps in the order of colours of the solar 

 spectrum. The plan recommended by the English committee differs considerably 

 in detail from that of Mr. Salter. 



5. 0)1 the Glacial Geologij of Central Wales. Btj Walter Keeping, M.A,, 

 F.G.S., Kee'per of the Yorlc Museum. 



Cardiganshire and the neighbouring counties of Central Wales form a moun- 

 tainous tract of country, consisting of rounded, grass-covered hills, often with 

 flattened peaty summits. Geologically, the district consists of monotonous repe- 

 titions of grit, and greywacke, shales and slates. 



The most important physical features are the two great planes of marine 

 denudation which limit the tops of the hills at heights of 500 ft. sloping up to 

 700 ft., and 1,100 to 1,500 ft. respectively. The drift-deposits range over both these 

 hill-groups, stretching up to within 100 ft. of the highest points. 



All the drifts in the central part of the district are of local origin, the materials 

 being derived from within the limits of the present drainage-areas. Glaciated 

 rock-surfaces are left in perfect preservation, excellent examples being seen in the 

 roches movtonnees of the Llyfnant valley, and many other places. The stony clay 

 or Till consists generally of a matrix of amorphous, stiff blue clay, crowded with 

 small angular grains and shaly fragments. This paste is thickly studded with 



' Jtejwrt of the British Association for 1847. Sections, f.9. 



