140 PKOCEEDINGS OF THE GEOLOGICAL SOCIETY. 



un con form ability *. One of the flows from this locality proves under 

 the microscope to be much more basic than the general type of these 

 rocks. Dr. Hatch informs me that it approaches to a basalt, con- 

 taining porphyritic crystals of fresh augite instead of the usual 

 felspars, and showing a groundmass of felspar microliths with some 

 granules of augite and dispersed magnetite. This local increase of 

 basic composition is interesting as occurring towards the top of the 

 volcanic group. A porphyritic and somewhat vesicular andesite with 

 large crystals of striated felspar in a dark almost isotropic ground- 

 mass occurs under the Coniston Limestone near Stockdale. 



Mr, Ward was much impressed with the widespread metamor- 

 phism which he believed all the volcanic rocks of this region had 

 undergone, and as a consequence of which arose the difficulty he 

 found in discriminating between close-grained lavas and fine tuffs. 

 There is, of course, a general induration of the rocks, while cleavage 

 has widely, and sometimes very seriously, affected them. There i& 

 also local metamorphism round such bosses as the Shap granite, but 

 the evidence of any general and serious metamorphism of the whole 

 area does not seem to me to be convincing. 



With regard to the original structure and subsequent alteration 

 of some of the andesitic lavas, an interesting section has recently 

 been cut along the road up Borrowdale a little south of the Bowder 

 Stone. Several bands of coarse amygdaloidal lava may there be 

 seen interstratified among tuffs. The calcite amygdules in these 

 rocks are arranged parallel to the bedding and therefore in the 

 planes of flow, while those lined with .chlorite are more usually 

 deformed parallel to the direction of the cleavage. This difference 

 suggests that before the cleavage took place 'the rocks had been 

 traversed by probably meteoric water producing internal alteration 

 and rearrangements, in virtue of which the vesicles along certain 

 paths of permeation were filled up with calcite, so as then to offer 

 some resistance to the cleavage, while those which remained empty 

 or which had been merely lined with infiltrated substance were 

 flattened and pulled out of shape. 



Though acid lavas are not wholly absent from the central and 



* This unconformability has been described and discussed by various observers. 

 The general impression has been, I think, that the break is only of local import- 

 ance. Mr. Aveline, however, believed it to be much more serious, and he 

 regarded the volcanic rocks which were ejected during the deposition of the 

 Coniston Limestone series as much later in. date than those of the Borrowdale 

 group. See Mem. Geol. Survey, Explanation to Sheet 98 JN.E., 2nd edit. p. 8 

 (1888). 



