568 Mr. J. Beete Jukes and the Eev. Samuel Haughton on the 



occur always as intrusive veins or dykes, forming the " elvan" dykes, which 

 pass directly into a variety of granite. 



Associated with the contemporaneous felstones and ashes are large masses 

 of greenstone of several kinds, which appear from their irregularity of outline 

 to be of more exclusively intrusive character than the felstones. Some of the 

 associated " ashes," however, resemble those of greenstone rather than of felstone, 

 rendering it probable that some at least of the greenstones are likewise of con- 

 temporaneous formation. Other masses and veins of greenstone also occur, at 

 a distance from any other igneous rocks, and clearly of subsequent and intru- 

 sive origin. 



Besides these, which we may call, for distinction's sake, trap rocks, granite 

 also occurs largely in our district : — 



1. As a large connected mass, exhibiting a great continuous surface, and 

 completely independent of any other igneous rock : 



2. As a number of small detached masses appearing here and there at the 

 surface, in more or less connexion with, or at least in near proximity to, the 

 trap rocks : 



3. At the south-eastern extremity of our district, forming apparently part 

 of another considerable independent mass, a great portion of which, however, is 

 covered by the sea. 



All the cranite now to be seen at tlie surface is of intrusive character and 

 of later date than the lower Pala30zoic beds with which it comes in contact, 

 as is proved by its sending veins into them, and by its having converted them 

 into metamorphic schists. 



We may, however, perhaps, be allowed to speculate on the probability of 

 molten granite having existed at no inaccessible distance beneath the surface, 

 during the deposition of the Cambro-Silurian rocks, and look upon the contem- 

 poraneous felstones as being the superficial products of this molten granite, 

 ejected either into the air, or into the seas, of those days. 



If it could be shown that the beds penetrated by the small detached masses 

 of granite mentioned above are considerably lower than the beds in which 

 the contemporaneous felstones lie, we might, perhaps, be pardoned for suspecting 

 that these detached bosses of granite formed part of the original molten mass 

 from which the flows of felstone proceeded. In this case we might look upon 

 the elvaus, perhaps, as the pipes or feeders along which the molten matter tra- 



