Correspondence — Mr. D, Mackintosh. 331 



Allusion was also made " to the greater certainty introduced into 

 the classification of the older formations, which enabled equivalents 

 to be recognized of the lower, middle and upper Cambrian of 

 Europe, and which also showed that the older Cambrian rocks had 

 been partially changed into gneiss and mica slate with andalusite, 

 and that a large part of the Silurian period is represented in the 

 Acadian provinces by volcanic rocks, quite dissimilar from the con- 

 temporaneous beds of the typical " New York Series," and more 

 resembling the English Skiddaw and Borrowdale rocks, while tliey 

 often have a very close resemblance to the older Huronian series 

 which exists in their vicinity." 



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EEPLT TO MR. USSHER AND H.E.H. 

 Sir, — I should not have troubled you with a reply to Mr, Ussher 

 were it not called for to preveut misunderstanding. I know nothing 

 of the age of the clay with flints, nor of the amount of denudation 

 which has occurred since its formation. While in Devonshire I was 

 under the impression that the gravels capping Blackdown extended 

 (unchanged in character) some distance down the slopes into the 

 valleys, and that the gravels with erratics on the summit of Little 

 Haldon extended continuously some distance downward on both 

 sides, and, on the east side, in patches as far as the sea-coast, in a 

 manner to me inexplicable by subaerial re-distribution. I thought 

 these gravels might possibly represent a part of the glacial drifts of 

 the N.W. and E. of England, and I now think it possible that the 

 older Devonshire gravels described by Mr. Ormerod, and lately in an 

 able paper by Mr. H. B. Woodward (Q. J. G. S. vol. xxxii.), may 

 have been accumulated during a part of the glacial period of the 

 N.W. and E. of England. Mr. Woodward's sections very strikingly 

 remind one of the mode of distribution of the glacial drift of the 

 N.W. which more or less conforms to the slopes of the valleys and 

 hills, and which is more a wrapper than a leveller of pre-existing 

 surface-inequalities. Of the age of these older gravels relatively to 

 the " Head " I cannot offer an opinion, but I have little doubt that a 

 part of the glacial period of the N.W. is represented by the " Head " 

 described by Mr. Pengelly, which covers or rather covered (for it 

 has been very much tampered with by man) the Miocene lignite and 

 clay of the Bovey basin. This " Head," which contained Arctic 

 plants, and great numbers of undoubtedly ice-borne boulders (one of 

 them 4 feet in average diameter (1867), has undergone an amount 

 of fluviatile and estuarine denudation extremely insignificant when 

 compared with the excavation of the Valley of the Exe or of the 

 pre-Miocene Bovey valley. The fact that the "Head" covers the 

 raised beaches of the SW. of England does not prove its post- 

 glacial age, because the date of these beaches relatively to those of 

 the N.W., and indeed of the latter relatively to the glacial period or 

 periods, is far from being certain. Mr. Godwin-Austen long ago 

 regarded the former as, in one sense, pre-glacial. Erom the Land's 



