Lower Pakeozoic Rocks of the South-East of Ireland. 



613 



Table XIV. 



Impurities added to 100 tons of Main Chain Granite, requisite to make Coollattin Granite, on the 

 supposition that a Bisilicate of Alumina is the form in which the Silica and Alumina are added. 



It follows from this investigation that if the clay slate added to the granite 

 have the composition assumed in Hypothesis B, that part of the potash of the 

 granite must have been washed out before it could have acquired the com- 

 position of the Coollattin granite. 



In the present state of our knowledge of the substances likely to have been 

 mixed with the granite of the main chain, when it broke through the Cambro- 

 Silurian slates of Wicklow, it would be extremely rash to place any reliance 

 on the foregoing, or, indeed, any other hypothesis. It is to be remembered 

 that the slate through which the granite penetrated is not a basic rock ; and, 

 therefore, we find the granite, although altered, still a genuine granite, and 

 the result of Hypothesis B applied to the granite of Coollattin is probable 

 enough. In the Carlingford district, where the rock penetrated by the granite 

 is limestone, the reaction on the granite is very different, as it is converted into 

 a syenite, highly crystalline, composed of anorthite and hornblende. 



III. Felspathic and Hoknblendic Traps. 



1. General Description. — In addition to the isolated granite patches already 

 described, which occur through the whole of the Cambro- Silurian rocks of 

 Wicklow and Wexford, there are many other patches of igneous or quasi- 



voL. xxm. 4 L 



