ORIGIN AND DEVELOPMENT OF ORE-DEPOSITS. 303 



other, from unknown depths in a molten state ; that it could be 

 upheaved with such force as to cleave asunder and throw back 

 the stratum of clay state, rise throughout its whole length 

 exactly to the surface and leave no impression of the effect of 

 intense heat, no signs of disturbance in the regularity of the 

 stratification or the uniformity of its dip. This elvan course has 

 recently been cut through in Dolcoath Mine 200 fathoms below 

 the surface. At that depth the breadth is still nearly the same 

 as at the surface ; the inclination of 45 is still preserved, and 

 the clay-slate on both sides rests as evenly against it as if it 

 were a mass of fleshy fibres surrounding an animal bone. Can 

 you believe such a theory with such facts as those before your 

 eyes ? I think not."* If we regard the elvans as injections of 

 granitic material in a semi-fluid (pasty) state into previously 

 formed fissures, most of the force of this able miner's objections 

 disappear at once.f Doubtless we must avoid confounding the 

 forces which produced with those which filled and perhaps 

 enlarged the fissure. 



Excluding a few elvans which have special directions, and 

 which at the same time be it remarked often have special 

 mineral characters, the most important elvans occur in four 

 natural groups, characterizing as many localities as follows : — 



1. The great series extending from Penzance to Truro ; 

 some of these elvans have been traced for 8 or 10 miles, their 

 general bearing is from 20 to 30 S. of W. 



Sub group {a.) Elvans of Carn Marth and north of Cam 

 Menelez. 



Do. {h.) Elvans of Perran-ar-worthal and south of 

 Carn Menelez. 



Do. {c.) Elvans of St. Agnes and Perran. 



♦Remarks on the Geology of Cornwall and Devon, Lecture 11, p. 13, (1859). 



f It will be remarked that Capt. Thomas himself falls into error in stating 

 the case. It may be that in the particular case he refers to, there are no signs of 

 disturbance in the regularity of the stratification of the country rock, but such 

 signs of disturbances are far from uncommon. Again he ignores some leading 

 "elements" of Physical Geology — effects of denudation and the like — when 

 he uses the words "rise throughout its whole length exactly to the surface." 

 Further, no one would expect the effects of intense heat which come from such 

 comparatiyely insignificant intrusions of moderately heated matter, probably 

 not more than 700 or 800° if so much, to be visible. 



