280 Geological Society. 



was that there was a fundamental difference in the classification 

 of tuffs and lavas. A large proportion of the Lake-District rocks 

 were brecciated, and had been supposed to be altered tuffs. With 

 the unbrecciated rocks into which they passed they had been 

 mapped as ashes. A number of specimens and photographs were 

 shown, indicating that the brecciation and apparent bedding were 

 due to flow. Specimens were also shown of explosion-breccias, of 

 the normal tuffs (which the Lecturer believed to be mainly the 

 result of erosion between eruptions), and of rocks simulating true 

 tuffs, but actually sandstones and conglomerates, composed of 

 detrital igneous material. Attention was drawn to the criteria for 

 distinguishing the various types. Recently, manuscripts had been 

 found in the possession of the Geological Survey proving that 

 Aveline, whose maps were extraordinarily accurate and detailed, 

 had anticipated by thirty years the Lecturer's separation from 

 the volcanic rocks of the basal beds of the Coniston Limestone 

 Series. 



When re-mapped on this basis, the Borrowdale Series appeared 

 as a simple and regular sequence, strongly folded and cropping out 

 in long bands. An interesting history of vulcanicity was revealed, 

 beginning in many places with explosion-tuffs followed by a great 

 series of pyroxene-andesites over the whole district. Then there 

 was a pause during which fine-grained andesite-tuffs, with a 

 tendency to produce true slates, accumulated. This was succeeded 

 by a vast outpouring of andesites, of great thickness in the central 

 mountain region, but dying out southwards and eastwards. Next 

 a series of peculiar mixed tuffs, of special value in mapping, was 

 covered by another mass of andesites dying out south-westwards. 

 After this, soda-rhyolites covered the whole district, nothing later 

 being preserved — with one possible known exception. These 

 volcanic rocks were intersected by a varied series of intrusions. 



The solfataric phenomena were of interest, including the pro- 

 duction of garnet and graphite, and a remarkable ' streaky ' 

 structure in the rhyolites. 



An important question related to the age of the large acid 

 intrusions associated with the volcanic rocks. Were they of the 

 same age as, or later than, the Devonian folding ? A sketch was 

 given of the evidence on which the Lecturer assigned the Eskdale 

 and Skiddaw granites to the Ordovician volcanic episode, and it was 

 suggested that the great Skiddaw anticline was not due to regional 

 folding, but a local structure connected with the vulcanicity. 



Lantern-slides of Lake District country were shown, and the 

 manner in which the volcanic rocks entered into the scenery was 

 pointed out. 



