Geological Society of London. 571 



trachytes, these old Cumbrian rocks might perhaps be called Felsi- 

 dolerites, answering in position to the modern Trachy-dolerites. 



A detailed examination of Cumbrian ash-rocks had convinced the 

 author that in many cases most intense metamorphism had taken 

 place, that the finer ashy material had been partially melted down, 

 and a kind of streaky flow caused around the larger fragments. 

 There was every transition from an ash-rock in which a bedded or 

 fragmentary structure was clearly visible, to an exceedingly close 

 and flinty felstone-like rock, undistinguishable in hand specimens 

 from a true contemporaneous trap. Such altered rocks were, how- 

 ever, quite distinct in microscopic structure from the undoubted 

 lava-flows of the same district, and often distinct also from the 

 Welsh felstones, although some were almost identical microscopically 

 with the highly-altered ashes of Wales, and together with them 

 resembled the felstone-lavas of the same country. 



This metamorphism among the Cumbrian rocks increases in 

 amount as the great granitic centres are approached ; and it was 

 believed by the author that it took place mainly at the commence- 

 ment of the Old Bed period, when the rocks in question must have 

 been buried many thousands of feet deep beneath the Upper Silurian 

 strata, and when probably the Eskdale granite was formed, perhaps 

 partly by the extreme metamorphism of the volcanic series during 

 upheaval and contortion. The author stated his belief that the 

 Cumbrian volcanos were mainly subaerial, since some 12,000 feet 

 of ash- and. lava-beds had been accumulated without any admixture 

 of ordinary sedimentary material, except quite at the base, con- 

 taining scarcely any conglomeratic beds, and destitute of fossils. He 

 believed also that one of the chief volcanic centres of the district had 

 been the present site of Keswick, the low craggy hill called Castle 

 Head representing the denuded stump or plug of an old volcano. 



The author believed that one other truth of no slight importance 

 might be gathered from these investigations, viz. that neither the 

 careful inspection of hand-specimens, nor the microscopic examin- 

 ation of thin slices, would in all cases enable truthful results to be 

 arrived at, in discriminating between trap and altered ash-rocks ; 

 but these methods and that of chemical analysis must be accom- 

 panied by oftentimes a laborious and detailed survey of the rocks in 

 the open country, the various beds being traced out one by one and 

 their weathered surfaces particularly noticed. 



Discussion.— Mr. Frank Rutley stated tTiat he had examined many of the 

 microscopic sections upon which much of the author's evidence was based, and he 

 believed that Mr. Ward was, in the main, correct in his conclusion that many of 

 the rocks designated trap were intermediate between dolerite and felstone, for 

 sections from one end of the series presented the character of tAie basalt, while 

 others from the opposite end appeared under the microscope to be true felstone ; 

 a variety of sections having also been cursorily examined which passed by almost 

 imperceptible gradations from the dolerites to the felstones. He considered that 

 Mr. Ward had done as much in the determination of these rocks as it was possible 

 to do by the examination of merely ready-mounted sections ; although, from this 

 method of investigation having been the only one at the author's disposal while 

 working in the field, he thought that the evidence regarding some of the com- 

 ponent minerals was scarcely satisfactory ; and he adverted to the importance of 



