890 



microscope this rock is seen to bo composed of deeply-coloured reddish 

 brown mica, white mica, quartz, opaquo rods and grains, andalusitc 

 and a few grains of colourless garnet. The reddish brown rnica is strongly 

 pleochroic and the minute inclusions are surrounded by deeply-coloured 

 borders. It is sometimes iutergrown with the white mica and both varieties 

 occur as plates of considerable si/.e. Andalusito occurs as small prisms and 

 large irregular masses. It occasionally shows the characteristic pleochroism. 

 The garnet is present only as an accessory constituent 



The Shap granite produces important alteration in the surrounding 

 rocks, but the nature of this alteration has not as yet been studied in detail. 

 Messrs. HARKNESS and NICHOLSON (1) call attention to the occurrence of 

 vesuvianito (idocraso) in a white crystalline limestone (Coniston limestone) 

 at Wastdale Head Farm. This mineral, as we have already seen, is 

 eminently characteristic of the contact metamorphism of limestone. 



Scotland. The granite masses of Kirkcudbright have produced 

 great changes in the sedimentary rocks with which they are associated, 

 and some information as to the character of these changes will be found 

 in the Survey memoirs. No descriptions of the microscopic characters of 

 the rocks have as yet, been published. In Skye, near Hroadford, Ordovician 

 limestone has been converted into white saccharine marble by contact 

 ineiainorphism, and vesuvianito is recorded from the same locality. 

 The marbles of Assynt, described by Dr. HKI>I>I,K,<-) maybe examples of 

 contact metamorphism for they occur in the immediate neighbourhood of 

 an extensive mass of igneous rock, and contain minerals (malacolite, 

 wollastonite, &c.) such as are known to be developed in limestone by the 

 action of igneous rocks. 



Ireland. The contact metamorphism produced by the Wicklow 

 granite has been described by Professor VON LASAULX.< :I) The lower 

 Paleozoic sediments become more and more crystalline as the granite is 

 approached. In the neighbourhood of Ivilliney the rock near the granite 

 is a micaceous schist. The principal constituents are quart/, two micas 

 and andalusite. The andalusite is especially abundant in certain layers. 

 Small prisms of brown tourmaline also occur. There appears to be no 

 development of typical hornfols. Mr. ALLPORT'S observation of the 

 occurrence of felspar in a contact-rock from Enniscorthy, Co. Woxford, 

 has been already referred to. 



The granites of northern Gal way appear to have produced important 

 alteration in certain limestones. Thus at Bimbeg the limestone near 

 the granite is highly crystalline and contains numerous garnets/ 4 

 Vesuvianito is also recorded from the altered limestones of Donegal. 



In this chapter \ve have referred more especially to the alteration 

 effected by granites and allied rocks. The contact metamorphism produced 

 by diabase or dolerite has already been described (see page 217). 



(1) (J.J.G.8., Vol. XXXIII., IS77. p. 466. 



(2) M.M.. issi. p. 'J71. 



(K) T.M.M. NYm> Kol-rr, K.-md I., p. IH.V 



(4) Dr. CALI.AWAY. Q.J.G.S., Vol. XLI., p. 'J'27. 



