1869.] NICHOLSON IGNEOUS ROCKS OF THE LAKE-DISTRICT. 439 



granite of the Caldew valley is nearly N.E. and S.W., and therefore 

 very nearly agrees with the strike of the Skiddaw Slates in this region. 

 The syenitic porphyry of Carrock Eell, on the other hand, appears 

 to extend itself in a direction from E. to "W., this being very 

 nearly the strike of the bedded traps of the green slate series by 

 which it is surrounded. Secondly, the mineral character of the 

 intrusive rock appears to vary with the character of the rocks which 

 surround it. Thus, high up in the valley of the Caldew we find a 

 coarsely crystalline granite lying in the heart of the Skiddaw Slates, 

 the latter being highly metamorphosed for a considerable distance 

 on both sides of the plutonic rock. As we approach the point where 

 the Skiddaw Slates are overlain by the green slates and porphyries, 

 the granite becomes much finer in grain and less highly quartzife- 

 rous. Finally, as seen in Carrock Pell, where it is surrounded by 

 the traps of the green slate series, it has entirely lost its granitic 

 character, and is now simply a felstone-porphyry. It contains 

 neither quartz nor mica, and is composed of a base of reddish fel- 

 spar, with crystals of felspar and specks of hornblende, closely re- 

 sembling, in fact, the syenitic porphyry of Buttermere. 



lY. Age of the Syenite of the Vale of St. John and the Felstone-por- 

 phyries of Buttermere and of Carrock Fell. 



In investigating the age of these igneous masses, an important 

 element of the inquiry is found in the discovery which I have 

 recently made (Geol. Mag. vol. vi. Nos. 3 & 4), that the green slates 

 and porphpies are superimposed unconformably upon the Skiddaw 

 Slates, an opposite opinion having been hitherto entertained. The 

 Skiddaw Slates, therefore, were subjected to elevation and denudation 

 before the formation of the green slates and porphyries had been 

 initiated. Bearing this in mind, it is, in the first place, noticeable 

 with regard to the three igneous masses in question, that they occupy 

 a definite and similar position in the stratified series of the Lake- 

 district. They are all found to be in relation, on the one hand, with 

 the Skiddaw Slates, a vast group of purely sedimentary origin, and, 

 on the other hand, with the green slates and porphyries, an equally 

 vast series of volcanic ashes and lavas. The second fact to be 

 noticed is that it is only the inferior sedimentary formation that is 

 metamorphosed, to any perceptible extent, by contact with these 

 intrusive masses. Of course, from the nature of the upper group, 

 any alteration which might be present would be much less conspi- 

 cuous than in the case of the Skiddaw Slates ; but I have not been 

 able to satisfy myself that there occurs any. The Skiddaw Slates, 

 however, are invariably metamorphosed in the neighbourhood of the 

 intrusive rock, this metamorphism aff'ecting in different localities a 

 greater or less thickness of the beds. In the vicinity of Buttermere 

 the alteration in the Skiddaw Slates is comparatively slight in 

 amount, and unaltered slates are found not many yards distant from 

 the intrusive rock. At the foot of Ennerdale, on the other hand, 

 the slates, in contact with the same rock, are altered throughout an 

 enormous thickness, the metamorphism being plainly visible at a 



