462 A. L. Leach — Glacial Drift and Rained Beach 



rock would be related to the detrital laterites referred to in the next 

 paragraph. Compared to the true laterites, the lateritoids, and the 

 detrital laterites, however, the lake laterites are probably of small 

 importance in India. 1 



{To be continued.) 



IV. — On the Relation ov the Glacial Drift to the Raised Beach 



NEAR PORTH ClAIS, St. DAVIDS. 



By Arthur L. Leach, F.G.S. 



DURING- a recent examination (August, 1911) of the glacial drifts 

 in the neighbourhood of St. Davids, I have noticed some glaciated 

 surfaces on boulders of the raised beach in a section on the coast 

 near Forth Clais, where the relation of the glacial Boulder-clay to the 

 raised beach is so clearly shown that (pending a fuller description 

 of these deposits) the importance of the section seems to justify 

 a preliminary notice. 



The raised beach of the Gower Feninsula has been described by 

 Mr. 11. H. Tiddeman, 2 who obtained definite proof that the beach 

 was pre- Glacial in the sense that it always lay below the glacial 

 drift in that district. The deposits associated with the raised beach 

 are grouped by Dr. A. Strahan 3 into a 'Raised Beach Series' 

 composed of three distinct members. The following brief description 

 of this series, as it is displayed in Gower, is taken from a paper 



1 I must point out here the logical sequence of the adoption of this term 

 lake laterite. If one is to apply the term to pisolitic iron-ores that have been 

 deposited by chemical precipitation from a body of water, and are, in addition, 

 associated with bodies of typical laterite, it is difficult to avoid its extension to 

 include those deposits of iron-ore, manganese-ore, and bauxite that have been 

 formed in an identical manner, but are not associated with lateritic rocks. All 

 the deposits classed as bog iron-ores and lake ores in textbooks on ore-deposits 

 could then be called lake laterites, and also the sedimentary manganese-ore 

 deposits. The lake iron-ores of Sweden, the bog iron-ores of various parts of 

 Northern Europe, the manganese deposits of the Caucasus, and perhaps the 

 iron-ores and bauxites of Antrim, must then all be classed as lake laterites of 

 various ages. Further than this, if my theory of the origin of the manganese- 

 ore deposits of the gondite series of the Central Province is correct (loc. cit., 

 pp. 308-19, 36-5), they are to be regarded as in part (the primary ores) the product 

 of metamorphism of a series of manganese-oxide sediments, chemically deposited 

 in lake basins, and interlaminated with mechanically deposited sands and clays, 

 the whole series representing a metamorphosed Caucasus (as has been noticed 

 by De Launay in his recent work La Gc'ologie et les Bichesses, Minerales de 

 1'Asie, p. 698, 1911). These Indian deposits are therefore metamorphosed lake 

 laterites. However, I do not wish to give this extended meaning to the term, 

 but insert this footnote merely to draw attention to the real significance of the 

 existence of the lake laterites, if any such can be proved to exist. There is to 

 me nothing objectionable in this term lake laterite, nor in its possible wide 

 extension as outlined above, if fellow - geologists think it desirable. This 

 possibility merely serves to point out the inherent chemical relationship between 

 the typical laterites and many deposits of iron, manganese, and aluminium ores 

 all over the world, which, whilst differing from true laterites in mode of 

 occurrence and formation, are yet related to them through the lake laterites as 

 defined in the body of this paper. 



2 Geol. Mag., Dec. IV, Vol. VII, 1900, p. 441. 



3 The Country around Swansea (Mem. Geol. Surv., 1907). 



