THE LAKE DISTRICT : GEOLOGY 133 



Igneous Rocks. — The Shap Granite, with its large pink crystals of orthoclase, 

 is well known architecturally. The intrusion has taken place near the junction 

 of the Coniston Limestone and the Borrowdale Volcanic Series, and since 

 associated dykes penetrate strata up to and including the Ludlow, and pebbles 

 of the granite are found in the basal conglomerate of the Carboniferous, the 

 age is closely defined. 



The chief interest in the Skiddaw Granite lies in the large aureole of 

 Skiddaw Slates converted into rocks ranging from chiastohte slates to 

 andalusite-cordierite-biotite homfelses, and the greisenisation in Grainsgill 

 accompanied by the development of quartz veins with tungsten. 



The Carrock Complex consists of a series of gabbros ranging from ilmenite- 

 rich to quartz-bearing, a hybrid diabase, a basified and a normal granophyre, 

 and a felsite. The order of intrusion is one of decreasing basicity and the 

 complex itself appears to be somewhat older than the Skiddaw Granite. 



Lack of space precludes more than a passing mention of the microgranite of 

 Threlkeld and the diorite of Embleton, though they are famous roadstones, 

 and of the Armboth Dyke and the minette of Sale Fell, but attention may be 

 drawn to the Ennerdale Granophyre and Eskdale Granite. Both are stock- 

 like masses occurring near the junction of the Skiddaw Slates and the Borrow- 

 dale Volcanic Series with portions of the original roof preserved : both show 

 some variations in type pointing to more than one intrusive phase, though it 

 is more marked in the case of the Eskdale Granite. Here the northern 

 portion is a pink perthitic granite with much quartz and muscovite, but little 

 biotite, whereas the southern portion has much biotite and many zenoliths, 

 and has obviously been basified. 



Carboniferous. 



The Conglomerates at the base of the Carboniferous have been claimed to 

 be of Old Red Sandstone age ; they possibly represent rock waste produced at 

 this period but deposited in the early Carboniferous sea. The most important 

 outcrops lie on the north side of the Lake District, but there are patches near 

 Kendal and Ulverston, and a conglomerate has been proved in mining near 

 Millom. 



The Cockermouth Lavas, a series of olivine basalts, succeed the con- 

 glomerates in places and are the only known representatives in the region of 

 Carboniferous igneous activity. 



The Limestone Measures of the Lower Carboniferous show considerable 

 variation. In West Cumberland there is about 700 feet almost entirely of 

 limestone ranging in age from S2 to D2, followed by a variable thickness of 

 shales and sandstones with thin limestones, of D3 age. In a north-easterly 

 direction this thick limestone develops a Yoredale facies and splits into several 

 bands separated by shales and sandstones. South-east and south of the Lake 

 District Garwood has shown that sedimentation began at an earlier date than 

 to the north and west, and the thick dolomites and limestones there range from 

 Z to Di, and are followed by D2-3 beds of Yoredale facies. 



The limestones of West Cumberland and Fumess are famous for their 

 metasomatic replacement by haematite, the iron of which was probably derived 

 from the associated Permo-Tnassic rocks. 



