Vol. 60.] ROCKS OF THE BORROWDALE VOLCANIC SERIES. 79 



of the Esk. The coarse rock dies out, and the rounded inclusions 

 become more rare until, when the western tributary is reached, 

 only the fine-grained rock remains, and it shows banding parallel to 

 the containing walls. 



Close to the western tributary and just below the path to Scaw- 

 fell Pike, a dyke 15 to 20 yards wide occurs : it is of a dark 

 colour, contrasting strongly with the white of the flinty ash into 

 which it is intrusive. Fragments of ash and basic xenoliths 

 weathering light-brown are not uncommon. There are, as usual, 

 fine-grained and coarse varieties, but all may be classed under the 

 head of quartz-porphy rites containing pinkish oligoclase-ande- 

 sine and altered ferromagnesian mineral. One section (3831) shows 

 a garnet with a margin almost entire and the faces well developed. 

 On one side corrosion has taken place, and here the felspar-crystals 

 are grouped round the garnet, together with apatite and a ferro- 

 magnesian mineral altered to chlorite, and epidote and iron-ore. The 

 occurrence of the felspar only on that side of the garnet at which 

 corrosion has taken place, seems to prove that the garnet has con- 

 tributed some constituent to the formation of the felspar, and not that 

 the garnet has simply acted as a convenient nucleus for the growth 

 of felspar-crystals. Ward continued this dyke in a northerly-and- 

 southerly direction to the junction of the two tributaries, where a 

 similar rock occurs. To connect the two together in a district 

 where dj^kes are so numerous, is perhaps somewhat speculative. 



III. Basic Offshoots from the Eskdalr Granite. 



In the Blea-Crag dykes every type of rock, from a basic porphyrite 

 to an acid granophyre, was found. I therefore wished to see whether 

 the Eskdale Granite-dykes yielded the same varieties of rock. A large 

 number of dykes are given off from the granite of Wastdale Head, 

 and may be well seen on the slopes of Great End and Scawfell Pike 

 to Lingmell Beck. Dropping down from the Sty-Head watershed, 

 excellent examples of rock bearing the greatest resemblance to Blea- 

 Crag rocks may be seen in Spouthead Gill. 



Going up the grassy tongue between Piers and Girla Gills, a 

 very typical dyke is met with 200 feet below Criscliffe Knotts. 

 The most basic rock is a fine-grained diabase, represented in 

 places by a greenish rock containing quartz, chlorite, epidote, and 

 phenocrysts of indeterminable felspar. 



The next type is a basic mica-porphyrite, with either 

 andesine or an acid labradorite, mica, and uralite. The section 

 (3855) is taken across the junction of the rock with the flinty ash. 

 Movement has taken place between the two, with the result that 

 the plagioclases are broken up into small fragments. 



The next in order is a coarse purplish rock, with greenish- white 

 felspar (3856). It is a quartz- porphyrite with altered 

 andesine, mica-flakes, and rare hornblende-crystals. The felspar 

 is altered to epidote and white mica. The groundmass consists of 



