34 METAMORPHIC ROCKS OP THE LAKE-DISTRICT. 



been subjected to the conditions of heat and pressure existing at a 

 depth of 50,000 feet are found not to be sensibly altered, whilst in 

 the same rocks the passage of a trap dyke caused a considerable 

 change in the mineral ingredients in its neighbourhood. The vol- 

 canic rocks described by the author were produced, Mr. Hicks 

 thought, in Silurian times. 

 Mr. Ward replied as follows : 



To Mr. Kiftley. — That the passage of the hypersthenite into the 

 felsite, though most decidedly gradual in some parts, was frequently 

 tolerably abrupt. 



To Prof. Hughes. — That Mr. Marshall's views as to metamorphism 

 were carried much too far, inasmuch as he considered the whole 

 volcanic series to represent beds of an ordinary sedimentary origin 

 highly metamorphosed. 



To Mr. Judd. — That the author had always endeavoured to be 

 especially on his guard against mistaking lines of viscosity in vol- 

 canic lavas and other rocks for indications of former bedding. He 

 defended the use of chemical analyses, when care was taken to 

 insure the analysis of truly typical and well-selected specimens, 

 adding that, although the results might not go for much when taken 

 alone, yet they were of some value if united with other lines of re- 

 search on the same rocks, such as microscopic and field examination. 

 With reference to deductions drawn from the examination of liquid- 

 cavities in the quartz of the granites, the author mentioned that 

 Mr. Sorby had expressed considerable surprise and satisfaction at 

 the general agreement of the author's results with those he had 

 published many years since on various granites other than those of 

 the Lake-country, and that a German physicist had arrived at 

 parallel results by an entirely different method of examination. 

 With regard to Mr. Judd's suggestion, that all or much of the 

 Lower Old Red may once have been present in the Lake-district, 

 thus adding to the thickness of rocks above the granite of Skiddaw 

 &c, Mr. Ward remarked that he would leave the Society to judge 

 whether we should consider that at the close of the Upper Silurian 

 some 20,000 feet of strata of Old Red age were deposited and then 

 denuded, or, considering there is no trace of these Lower Old Eed strata 

 in the district, whether at the close of the Upper Silurian, when the 

 Skiddaw Slates were covered by some 20,000 feet of strata, that 

 vast denudation alone took place, which bared the rocks round 

 Skiddaw, and was succeeded by the deposition of only the upper- 

 most beds of the Old Red. 



To Mr. Hicks. — That he was of opinion that it was rather too 

 strong a statement to make, that because certain beds buried — as 

 Mr. Hicks affirmed — under 50,000 feet of strata were not much 

 metamorphosed, therefore no granite could be formed at a less depth 

 than this ; he believed that the Lake-district work completely con- 

 futed such a statement. 



