NOTES AND COMMENTS 



LAKE DISTRICT ROCKS. 



At a recent meeting of the Geological Society of London, 

 Mr. J. F. N. Green delivered a lecture on thq Igneous Rocks 

 of the Lake District. He first drew attention-to softie of the 

 manuscript 6-inch maps of the Lake District, prepared nearly 

 fifty years ago, by the Geological Survey, and pointed out that, 

 although undoubtedly most accurate, they differed greatly 

 in the volcanic area from his own. He suggested that the 

 reason was that there was a fundamental difference in the 

 classification of tuffs and lavas. A large proportion of the 

 Lake- District rocks was brecciated, and had been supposed to 

 be altered tuffs. With the unbrecciated rocks into which they 

 passed they had been mapped as ashes. Several 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. 



VULCANICITY. 



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 Vul- 

 canity 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. 



PROF. W. BOYD DAWKINS. 



In presenting the Prestwich Medal, awarded to Prof. W. 

 Boyd Dawkins, at the anniversary meeting of the Geological 

 Society of London, the President stated : ' During fifty-six 

 years Prof. Dawkins has contributed nearly thirty papers to 



1918 May 1. 



