On the Geology of the Lake District. 467 



mass, or the new conditions under which the minerals have been 

 brought into contact with the sedimentary rock, which has produced 

 the change, and tlien point out that both the one and the other may 

 be obtained by a sufficient depression of the sedimentary rocks. 



The author next describes the Coniston Limestone, which consists 

 of dark greyish blue slates and shales, with bands and beds of impure 

 limestone of varying thickness and irregular occurrence. It ap- 

 parently overlies the Green Slates and Porphyry conformably, with 

 beds of rather an intermediate character between ; but as the passage 

 beds consist in a great measure of soft slates, the junction is mostly 

 obscured. Tliis formation is universally allowed to be the equivalent 

 of the Bala Limestone. 



There is considerable difference of opinion, however, as to where 

 we should draw the line between these Bala beds and the overlying 

 Coniston Flags and Grits. Professor Sedgwick published, as the 

 result of his original field work, the view that the Flags and Grits 

 were the commencement of an entirely different group, and if we 

 look at Prof. Ramsay's Geological map of England and Wales, we shall 

 see how naturally the sweep of the Denbighshire Flags and Grits 

 resting, as first shown by Professor Sedgwick, unconformably upon 

 the Bala beds in North Wales, would, if prolonged, include the 

 mass of Coniston Flags and Grits in the Lake District ; while the 

 general character of the Flags and Grits is so similar in both cases 

 that there is much to suggest that the Coniston Flags and Grits bear 

 the same relation to the Coniston Limestone that the Denbighshire 

 Flags and Grits do to the Bala Limestone. Prof. Harkness and Dr. 

 Nicholson include the Flags and Grits with the Coniston Limestone 

 in the Lower Silurian, and consider them as higher beds of the Lower 

 Silurian series than any exposed in Wales. One of the officers of the 

 Geological Survey, wishing to have the question discussed by those 

 acquainted with the district, has, with the permission of the Director 

 of the Survey, anticipated their official publications to point out in a 

 paper in this Magazine, that the result of his mapping as far as it 

 went, tended to show that the original classification of Professor 

 Sedgwick was right. (Geol. Mag., 1867, Vol IV., p. 346.) 



This makes a difference of, at least, 6,000 feet in the position of 

 the base of the Upper Silurian rocks. It will appear, at once, from 

 the statement of the points at issue, by Dr. Nicholson, that we re- 

 quire more evidence as to the stratigraphical relations of the beds 

 at the base of the flags before we can consider the question settled. 

 It seems most improbable that the fossils in the two lists, given on 

 p. 62, can have come from the same beds. 



The Coniston Grits pass up very gradually into slaty and flaggy 

 beds, to a part of which the name Bannisdale Slate has been given ; 

 and, although they are, undoubtedly, only part of the Coniston Grit 

 series, they form a division as useful and as marked as the Flags into 

 which the Coniston Grits pass down. Our author, having shown 

 that in some cases what were supposed to be flaggy beds above the 

 Coniston Grit, are, in reality, only the Coniston Flags, repeated by 

 faults or folds, drops the Bannisdale Slates altogether; but there 



