ASSOCIATED METAMORPHIC ROCKS OF THE LAKE- DISTRICT. 33 



by pressure. The nature of felsitic matter was not, in his opinion, 

 well understood. In many instances it is exceedingly difficult to 

 distinguish between mica and hornblende, hornblende and mica 

 plates of microscopic size being much alike under certain circum- 

 stances. He had never seen lines of bedding in hypers thenite as 

 described by the author. Quartz-porphyry and rocks of that de- 

 scription were merely varieties of granite. The felsitic dykes 

 occurring in the Upper Silurians of the Lake-district nearly all 

 contain magnesian mica. He thought it a curious fact that, although 

 the Carboniferous Limestone must at one time have overlain a great 

 part of the Silurian rocks of the Lake-district, there are no traces of 

 the typical doleritic dykes of the Carboniferous Limestone in the 

 latter rocks, through which, however, the dykes must in the first 

 instance have passed ; and it would be interesting to ascertain what 

 was the mineral constitution of basalt dykes of Carboniferous age 

 where they passed through underlying sub-Carboniferous rocks. 

 The spots in the specimens described by the author as " Spotted 

 Slate " appear to be crystals. 



Prof. Hughes drew attention to a paper by Mr. Marshall on the 

 metamorphism of the Lake- district, which he considered correct in 

 principle, though in the application the author might be often wrong. 

 He thought that we should be cautious not to attach too great 

 importance to the apparent dip of metamorphic rocks to or from a 

 granitic boss or ridge, as the phenomena might be produced during 

 movements at any period subsequent to the consolidation of the 

 granite by the greater compressibility of the surrounding rocks as 

 compared with the granite, the extreme of this action producing 

 the protrusion of solid granite, also that the withdrawal of a large 

 amount of matter from below to furnish the materials of the volcanic 

 ejectamenta must cause extensive sinkings of the area from below 

 which this matter was withdrawn. He gave examples, on a small 

 scale, of what Mr. Ward had termed selective metamorphism, and 

 showed that, in the case of the Whin Sill, it seemed to affect most 

 the more siliceous rocks. He also referred to examples of certain 

 mica-trap dykes on the borders of the Lake -district, the mode of 

 occurrence of which suggested that they were due to the alteration 

 of the Silurian rock in place along lines of joints. 



Mr. Judd maintained that the relations of the igneous to the 

 stratified rocks of the Lake-district, which had been rendered so 

 clear by the author's surveys, were perfectly consistent with a 

 totally different conclusion from that at which he had arrived ; and 

 he doubted whether the chemical analyses cited in the paper could 

 really be regarded as bearing out the author's views. With respect 

 to the application to the district of Mr. Sorby's deductions from the 

 study of liquid- cavities in the crystals of igneous rocks, he argued 

 that (as many of the necessary data employed in the solution of the 

 problem were confessedly only the rudest approximations instead of 

 actual values) but little importance could be attached to the results 

 arrived at. 



Mr. Hicks remarked that, in the Cambrian series, rocks which had 

 Q. J. G. S. No. 125. d 



