440 • PEOCEEDINGS OP THE GEOLOGICAL SOCIETY. [June 23, 



distance of half a mile from the syenitic porphyry. In the Caldew 

 valley the metamorphism is still greater, and affects a much greater 

 thickness of the beds. 



In the third place, the intrusive masses show a great similarity in 

 their mineral characters. They are all highly felspathic, and the 

 chief difference between them is in the amount of free quartz which 

 they contain, this being, however, variable in different portions of 

 even the same mass. In the syenite of the Yale of St. John, the 

 amount of quartz is tolerably large ; but in the syenitic porphyry of 

 Buttermere quartz is much more sparingly developed ; and in the 

 felstone-porphyry of Carrock Eell it appears to be entirely wanting. 



Pourthly, the series of the green slates and porphyries, where it 

 comes into relation with these intrusive rocks, is distinguished by 

 the absence or thinness of the breccias and ashes, and by the great 

 development of the bedded traps, the former expanding and the 

 latter diminishing in thickness as we get at a distance from the 

 intrusive focus. Thus, the syenite of the Yale of St. John is suc- 

 ceeded to the south by the great series of bedded traps, which extend 

 to the foot of Thirlmere, the breccias and ashes of Borrowdale and 

 Watendlath having entirely thinned out, though they are of great 

 thickness and are situated only a few miles to the S.W. In like 

 manner the felspathic trap, which usually forms the base of the 

 green slate series, and which is generally of small thickness, appears 

 to expand enormously in thickness to the S.W. of the syenitic por- 

 phyry of Ennerdale, as is seen in the valley of the Liza. Lastly, 

 the felstone-porphyry of Carrock Fell occurs in connexion with the 

 well-known series of bedded traps which compose the Caldbeck 

 Fells, and which constitute the inferior portion of the green slates in 

 this region. 



Fifthly, in the case of one of these intrusive rocks (the felstone- 

 porphyry of Carrock Fell), it seems tolerably certain that there is a 

 gradual passage from a felstone, through a fine-grained granitic 

 rock, into a genuine granite. 



Taking the above-mentioned facts into consideration, it appears to 

 me that two theories only could well be advanced to account for the 

 relations which subsist between these intrusive masses and the 

 stratified rocks which lie around them. 



It might be held, in the first place, that these intrusive rocks 

 belong in reality to the Skiddaw Slates, the date of their production 

 coinciding with the period in which the Skiddaw Slates were prima- 

 rily elevated, anterior to the commencement of the deposition of the 

 series of the green slates. In this case the green slates and porphy- 

 ries would be subsequently deposited upon a denuded surface formed 

 partially of Skiddaw Slates and partially of intrusive igneous rock. 

 To this view there are various objections, the chief being that the 

 intrusive rock in some cases appears to penetrate the superior for- 

 mation by which it is almost entirely surrounded, as is the case with 

 the felstone-porphyry of Carrock Fell. 



The other theory has been well expressed by Professor Eamsay 

 (Mem. Geol. Survey, vol. iii. p. 235) with regard to some of the in- 



