Correspondence — C. D. Sherborn § J. Allen Hoive. 573 



The Gopeng Beds, consisting of clays and boulder-clays with some 

 stratified drift, are of glacial origin. This is proved by the inclusion 

 of large boulders in the clay, by the physical condition of the com- 

 ponents of the clays and their distribution, and by the striking 

 resemblance of the beds as a whole to Pleistocene glacial detritus. 



The nature of the beds is considered to be sufficient proof of glacial 

 origin, but it is admitted that no boulders have been found showing 

 striation due to ice-action, nor has any glaciated rock-surface been 

 found. Such evidence, however, can hardly be expected, because the 

 boulders are all more or less decomposed owing to the great power of 

 the ground-water in removing silica; and, if the limestone ever 

 presented the features of a glaciated surface, it has been so much 

 modified by solution owing to the action of ground-water since then, 

 that all traces of those features must have disappeared. Large 

 unweathered boulders of corundum are present in some of the beds, 

 but their hardness would make the appearance of ice-scratches 

 improbable. 



Unfortunately the pale and uniform colouring of the bulk of the 

 clays and boulder-clays makes it hard to obtain photographs showing 

 clearly the resemblance to Pleistocene glacial deposits. A number of 

 photographs is submitted, however, that will, it is hoped, do some- 

 thing towards this. The petrology of the Gopeng Beds is described 

 in detail. The most interesting point revealed is that the ice from 

 which the detritus was derived passed over a stanniferous granite 

 mass, and in consequence the Gopeng Beds carry tin-ore throughout, 

 though sometimes in very small quantities. This tin-ore is an original 

 constituent of the beds, but they have been, further enriched by tin- 

 ore derived from the Mesozoic granite at their junction with the 

 granite and in the neighbourhood of veins from the granite that have 

 risen through the limestone. 



The faulting in the Gopeng neighbourhood, the general structure of 

 the country, and the age and origin of the Gopeng Beds are discussed 

 in detail. The Gopeng Beds are considered to be the equivalent in 

 time of the Talchir boulder-beds of Orissa; but a penological 

 similarity is wanting, because the Gopeng Beds were derived from 

 a mass of stanniferous granite, the position of which is at present 

 unknown. 



COEBESPOITDE]SrCB. 



THE CULM-MEASUEES OP THE EXETEE DISTEICT. 



Sir, — In the last number of the Geological Magazine, pp. 495-7, 

 Mr. Arber, when criticizing Mr. F. G. Collins for doing things he has 

 not done, and for omitting others that he has done, has allowed himself 

 to commit a double error. 



It is clear from a glance at Mr. Collins's paper 1 that the words 

 Mr. Arber quotes, and to which he objects, are not those of 

 Mr. Collins at all ; they relate solely to the fauna which Mr. Crick 



1 Quart. Journ. Geol. Soc, vol. lxxvii, pt. iii, p. 393, 1911. 



