144 ASSOCIATION OF [Ch. VIII. 



of their junction with the containing schists: they, in fact, 

 display all the phenomena which occur at the junction of the 

 main masses of granite and slate. Thus, the elvans often pro- 

 trude or bulge out in the form of angular or rounded pro- 

 tuberances, which sometimes appear to be separated from the 

 course by open seams, which run parallel with the regular 

 part of the elvan, and continue uninterruptedly in the same 

 line ; so that if the projecting portion be small, it will often be 

 found to form a part of the adjacent schistose concretion ; they, 

 likewise, are sometimes elongated into lateral branches, or 

 terminate in minute strings, after the manner of veins ; 

 and it is no uncommon occurrence for insulated pieces of the 

 elvan to be imbedded in the slate, and, vice versa, for those of 

 the latter rock to be contained in the former. 



For farther particulars concerning the situation of these 

 granitic beds in the slates, we must refer to the fourth and 

 fifth chapters : those details ought to have been given in the 

 present chapter, but by so doing we should have separated 

 from them one of the most characteristic features of the schis- 

 tose rocks, and thereby rendered the description very im- 

 perfect. 



Besides these somewhat regular beds or courses of granitic 

 rocks, irregular masses or bunches of various dimensions also 

 occur in the primary slates. These are particularly abundant 

 near the junction, as is well illustrated on the sea-shore near 

 the village of Mousehole, in Cornwall ; where they are seen to 

 be connected with the slate on all sides, sending out veins, 

 passing into the slate by mineral gradations, forming, with 

 portions of the slate, the same concretions, and also containing 

 insulated pieces of slate of different sizes and shapes. It might 

 be contended that these bunches of granite are merely pro- 

 tuberances of the subjacent granite : in some cases, even at 

 Mousehole, they probably are ; but that they are not always 

 so, is demonstrated by the workings of Dolcoath mine, where 

 several of these outlying masses of granite have been found 

 to be perfectly insulated. 



