94 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 1 894, 



very fully treated from this Chair, it is not my purpose to deal with 

 pre-Cambrian volcanic rocks on the present occasion, except in part 

 as to their possible relations with the sedimentary series. 



When we bear in mind that the pre-Cambrian volcanic series is 

 of considerable importance, its elimination materially diminishes 

 the amount of matter which has to be dealt with. Practically we 

 are limited to the sedimentary series and to a portion of the crys- 

 talline schists. There have, of course, during the past seven years 

 been a very great number of papers of a more or less petrological 

 nature, where the rocks described may or may not belong to the 

 Fundamental group. The following authors, however, have written 

 papers on rock-groups whose position below the fossiliferous Cam- 

 brian cannot be doubted. These are Messrs. Peach and Home, 

 Blake, Callaway, and Butley, and Miss Raisin. The bulk of this 

 literature relates to Wales and Anglesey, but Shropshire and the 

 Malverns come in for a fair share. 



Oddly enough, the best defined pre-Cambrian, or Fundamental 

 sedimentary series, is to be found in the North-west Highlands, a 

 district which only a few years ago was an enigma, but which we 

 hope may now supply a clue to regions apparently more obscure. 

 At length geologists have discovered a pre-Cambrian system which 

 has a well-defined base and an equally distinct summit. It may be 

 said that this is no discovery, after all, since the Torridon Sandstone 

 has attracted attention ever since the days of Nicol and Murchison. 

 But we owe to Messrs. Peach and Home, in the first place, the clearest 

 proofs that the Torridon Sandstone is unconformable to the overlying 

 system, a fact which was disputed in the ' Quarterly Journal ' not very 

 many years ago. Secondly, the same authors having demonstrated 

 on palaeontological grounds the Lower Cambrian age of the over- 

 lying series, it follows that the Torridon Sandstone, though entirely 

 sedimentary and unmetamorphosed, is of pre-Cambrian age, and 

 there seems no reason why it should not prove to be fossiliferous. 

 Indeed, hopes have been expressed that a fauna might be discovered, 

 but as yet I have not heard of these hopes having been realized. 



It would appear that there is a considerable amount of variety, 

 within the area, in the formation known as the Torridon Sandstone. 

 As far as I myself remember it, the grits partake very much of the 

 nature of an arkose, showing that the felspar-fragments had not 

 suffered extremely from kaolinization,and thus pointing to rapid accu- 

 mulation. Much of the material appears to have been derived from 

 rocks similar to the underlying Lewisian gneiss. In the far North- 



