112 Marker : Appendix on the Igneous Rocks. 



It is a red, fine-grained rock, with conspicuous large crystals 

 of white mica, besides quartz-grains and flakes of black mica. 



The Mica- Lamprophyres. — There are numerous small dykes 

 and sheets of mica-lamprophyre in western Yorkshire and 

 eastern Westmorland, and their approximate age is fixed by 

 the fact that they traverse all the Lower Palaeozoic strata, but 

 never enter younger formations. The best-preserved example 

 makes an irregular intrusion in Swindale, and is easily recog- 

 nized by its abundance of dark mica. Like other occurrences 

 of this group of rocks, it encloses scattered grains of quartz, 

 more or less corroded. 



The Whin Sill. — This is the most southerly example of a 

 group of sills and dykes of late Carboniferous or Permo-Car- 

 boniferous age, largely represented in the southern half of 

 Scotland. The rocks are quartz-dolerites. What is seen in the 

 Carboniferous escarpment at High Cup Nick is merely the 

 western termination of a thick sill, which can be traced as far 

 as the coast of Northumberland and the Fame Isles. The 

 very coarse variety of the rock, as exposed in Teesdale, is not 

 seen here. 



Carrock Fell District. 



Ordovician Volcanic Rocks. — The Volcanic Series, as it 

 occurs on the north side of Carrock Fell, is represented chiefly 

 by basic lavas of a type which makes a large spread in the 

 Lake District. They are basalts, without olivine, but often 

 containing little pseudomorphs after hypersthene. They are 

 best seen in Eycott Hill, and the most striking variety there 

 is one containing large porphyritic felspar crystals (labradorite- 

 bytownite). In Drygill, associated with strata of the Coniston 

 Limestone group, are some relics of rhyolife lavas, much altered 

 and poorly exposed. 



The Carrock Fell Intrusions.— The higher ground here is 

 made by two laccolitic intrusions, one of basic and the other 

 of acid rock. On the south side, and extending westward for- 

 some miles, is a coarse gabbro. It varies much in composition, 

 with gradual passage from one variety to another. The central 

 portion is a quartz-gabbro, and the rock becomes progressively 

 more basic towards its margin, the actual edge being made by a 

 remarkably dense and dark variety, rich in titaniferous iron- 

 ore. Enclosed in the heart of the gabbro in numerous places 

 are patches of basalt, like that of Eycott Hill, much meta- 

 morphosed. North of the gabbro, and making the summit 

 of the hill, comes a granophyre, intruded later than the gabbro, 

 and partly overlying it at a steep inclination. It is a relatively 

 pale and fine-textured rock, but becomes richer in the dark 

 minerals towards the southern (or lower) edge. Where it 

 comes into contact with the peculiar basic margin of the gabbro. 



