Vol. 60. ] ROCKS OF THE BORBOWDALE VOLCANIC SBBIE8. 95 



angles between contiguous felspars. This would hardly occur if 

 the garnet and the felspar-growth were thrown out together. 



Before proceeding further, it may be well to describe a few typical 

 examples of ' streaky' rocks. The lowest rock of the series exposed 

 on llosthwaite Fell is a light-green rock with pinkish-white felspar 

 in abundance. This is seen in section (3780 : PI. XIV, fig. 1) to 

 be a plagioclase, much altered to calcite. Fragments of a grano- 

 phyric rock occur, showing a pretty micrographic intergrowth and 

 needles of chlorite representing original hiotite. These granophyre- 

 fragments resemble very closely the Euttermere Granophyre. We 

 have, then, another piece of evidence, besides the occurrence of 

 garnet, which serves to show how closely connected the rocks of the 

 Volcanic Series are with the garnet-bearing rocks intrusive in them. 

 In addition, fragments of an andesitie groundmass, with diffused 

 iron-ore, are also present. The matrix is felspathic, and minute 

 felspar-fragments occur with concave outlines. The rock may thus be 

 called a tuf f-porphy roid. Garnets with exquisitely-bright faces 

 are common. Purplish flinty fragments as well as dark chloritic 

 basic portions occur; it is the squeezing of the latter that gives 

 the ; streaky ' character to the rock. 



Other types are found, in which the 'streaky' character is 

 due to thin lines of green chloritic matter (3772). Phenocrysts of 

 plagioclase occur at all inclinations to these lines, which are often 

 bent as if the felspar had fallen on them from above. This chloritic 

 matter is original, and not produced by infiltration. Punning across 

 the streaky lines are others, formed also of chlorite or more rarely 

 of chlorite and quartz. These are true veins, infiltration having 

 occurred along lines of faulting, for the vein may be seen to pro- 

 duce displacement of the fragments of a felspar through which it 

 may pass. 



At other times, the streaks are broader, and consist of a coarse 

 felspathic matrix impregnated with quartz, chlorite, and calcite 

 (3870). Aggregates of calcite are very characteristic of this class 

 of rock, as well as skeleton-crystals of ilmenite enclosing a green 

 or greenish-brown, pleochroic, serpentinous mineral. This occurs in 

 the ' streaky ' rocks of Borrowdale and Haweswater alike. 



Another type of ' streaky 'character consists of lenticular fragments 

 of quite different petrological and chemical composition. Such a rock 

 is shown in the microphotograph (3S7-3 : PI. XIV, fig. 2) and occurs 

 at Hindside, Seathwaite. A similar rock is to be found on the lower 

 slopes of Scawfell. Yellowish- white lenticular patches of rhyolite 

 occur, separated by a darker and more basic fine-grained matrix. 

 These rhyoli.tic aggregates contain felspars, probably oligoclase or 

 oligoclase-andesine, in the usual felsitic paste. The felspars are, 

 however, not peculiar to the rhyolite-fragments, but occur through- 

 out. Tufts aud wisps of an almost colourless mineral occur, giving 

 bright polarization-tints. This mineral is associated closely with 

 chlorite, aud seems to pass into it. The same mineral, which I am 

 unable to identify, occurs abundantly in the Haweswater rocks. 



