Ch. II.] ELVAN-COURSES. <23 



tween these two forms of elongated masses of granitic rocks. 

 In composition, these elvans are either shorl-rock, eurite, fel- 

 sparite, or even varieties of fine-grained granite. They are 

 particularly abundant in the Land's End district : and their 

 presence is generally indicated by the abundance of tabular 

 and very angular stones in the hedges and farm-buildings. 

 These courses sometimes correspond or are parallel with the 

 layers of common granite in which they are situated ; but at 

 other times they intersect these layers or beds, after the man- 

 ner of the elvans in the schistose rocks. Notwithstanding, 

 however, this apparent irregularity of arrangement, the elvans 

 are connected on either side with the granite by the most 

 intimate mineral gradations, or contain irregular portions or 

 masses of the common granite, with which they also coalesce. 

 Other marks of the close connection which subsists may be 

 enumerated ; such as the penetration of both rocks by felspar 

 crystals, and similar appearances observed in granite veins : 

 but one of the most important was described lately by the 

 Rev. George Pigott, in a paper read at the last annual meet- 

 ing of the Cornish Geological Society ; viz. the continu- 

 ation of the small veins or stripes of shorl through both 

 granite and el van; and also the extension of one of the 

 parallel layers of granite itself through the elvan, at Pedn- 

 merer-mere, near the Logan Rock. 



The alternation of soft and hard granite, so common in 

 several parts of Cornwall, is of the same nature. The former 

 frequently contains parallel contemporaneous veins of quartz 

 and shorl, which abound in tin ; and, when this is the case, 

 the layer of granite containing the ore is considered by the 

 miner as the lode. Sometimes, indeed, these veins are so 

 numerous that it is necessary to excavate the whole of the 

 rock, like the stockworks of the Germans ; as at Carclaze 

 mine, and the old workings of Beam mine, near St. Austle. 



