526 Correspondence — Mr. J. G. Goodchild. 



THE CONISTON LIMESTONE SERIES. 



Sir, — The Geologists Association visited the exposures of the 

 volcanic rocks on the iianks of Roman Fell unrler my guidance, on 

 the occasion of the Long Excursion to Cumberland in 1889, when 

 they had an opportunity of examining the sections which it was the 

 chief object of my paper on the Coniston Limestone series to describe. 

 Other field geologists have at different times examined the same 

 facts with me. The sections are not very easily found, and the 

 relation of the various rocks to each other is certainly not very clear 

 at first sight. But after repeated examinations of the Ordoviciau 

 rocks of the whole of the area enclosed by the Pennine Faults it 

 becomes evident that there are three well-marked horizons on which 

 volcanic rocks occur. The highest of these is intimately associated 

 with the base of the Coniston Limestone. " The lowest consists of 

 a series of tuffs of subaqueous origin, which are clearly interstratified 

 with argillites resembling the Skiddaw Slates. These are the rocks 

 of the Milburn Series, and are the submarine equivalents of the 

 lower half of the Borrowdale volcanic series. Tlie third includes 

 the very peculiar set of volcanic rocks which I have described as 

 the Helton Moor volcanic series. These are quite different in litho- 

 logical character from either of the other two, and as they cannot be 

 newer than the first, nor older than the second, they must be of age 

 intermediate between the two. All three types occur side by side 

 on Helton Moor, as I have pointed out already on several occasions. 

 It is in association with these that the shales of Lycum Sike occui*. 

 We have the best possible authority for the occurrence in these beds 

 of Lycum Sike of Trematis corona, which occur also in the shales 

 belonging to the Coniston Limestone Series. Trematis corona is 

 here, therefore, not available as a characteristic fossil, for the beds 

 of Lycum Sike are separated by a consideral)le. if unknown, thick- 

 ness of other rocks from the true Coniston Limestone Series^ This 

 latter overlies the rocks of Dufton and Knock Pikes, while the beds 

 of Lycum Sike lie at an unknown distance below. 



Much more is involved in this question than a mere error of 

 delineation, which no one who has attempted to map the complicated 

 area in question could well avoid, here or there. 



Unless I am very greatly mistaken it is the middle and the upper 

 group of these volcanic rocks which occur at the northern end of the 

 exposure near Melmerby, and it is the same two groups which form 

 the volcanic groups on the north-east side of the Lake District. And, 

 furthermore, I strongly suspect that there is a considerable uncon- 

 formity between the two higher, or Bala, volcanic groups, and the 

 Arenig and older rocks upon which they lie in Cumberland. 



I have little doubt that the Ordovician tuffs of the Craven area 

 also correspond to those of Helton Moor and Dufton ; but whether 

 the Ingleton Green Slate series lies unconformably below these, or 



1 I regret very much that I did not write to Prof. Lapworth regarding what I 

 understood him to say about the two horizons of Trematis corona at Girvan. I did 

 not like to trouble an exceptionally busy man upon a matter that I thought he had 

 already stated quite clearly. The error is mine. 



