78 Prof. Liveing, On the metamorphism [Oct. 29 



been formed at a time when tlie direction of the pressure below 

 was such as to open a different line of joints. I believe they are of 

 much older date than the greenstone dykes, and that they have 

 undergone a certain amount of metamorphosis whereby the por- 

 phyritic character has been imparted to them. 



The gneiss in contact with them appears at least in places to 

 have become indurated, the stratification is not at all obliterated, 

 but the rock has acquired more of a hornstone character, is less 

 crystalline and perhaps contains a larger proportion of quartz; 

 a change not produced by mere heating, as it is very unequally 

 distributed. 



One point to which I wish to draw particular attention is the 

 extreme variation in the amount of metamorphism which the rocks 

 have undergone within a very short distance. 



The pink syenite of Cobo I thought at first must be intrusive, 

 it is so highly crystalline and so entirely devoid of stratification; 

 but it really seems to be only an altered state of the red gneiss. 

 In the first place they quarry grey syenite, elsewhere proved to be 

 stratified, at a very short distance, a few hundred yards north from 

 the pink stone, and the quarrymen assured me in a very positive 

 manner that none of the pink was to be found under the grey, 

 however deeply they might go into it. 



Moreover, in one quarry there are patches of grey in the pink 

 stone, as if the original beds were there somewhat intermingled, as 

 they are in the bay under Fort George and under Cornet Castle. 

 On tracing the gneiss down the north side of the Vazon Bay Road 

 it becomes very hard under the small square white-washed tower 

 called the " Hougue," and gradually loses its stratified character as 

 it passes westward. The stratification is obliterated without any 

 material change in the mineralogical characters. The colour 

 and texture of the rock into which it passes here are not the 

 same as at Cobo, it is greyer and less coarsely crystallized ; but the 

 material of the Cobo rock is so nearly the same as that of a great 

 deal of the gneiss, that apart from the complete obliteration of the 

 stratification there is no difiiculty in the identification of the two. 

 In fact, the Cobo rock mineralogically belongs rather to the 

 upper, more quartzose beds than to the lower hornblendic beds. 



These lower beds are quarried all over the northern part of the 

 island. The land there is generally low, but has a number of 

 bosses of rock projecting above the general level. These are harder 

 or tougher parts which have resisted the weather. Most of the 

 quarries have been begun in these bosses, but it is often only when 

 they have got well down, or well into the hill, that stone suitable 

 for breaking into square blocks is found. The bosses are often full 

 of veins and cross joints, and coarsely crystalline patches. These 

 patches the workmen call " sunburnt," imagining their coarse tex- 



