52 Miss M. K. Andrews en 



junction, where the two rocks are united into so hard a mass, 

 it was difficult to obtain specimens. Towards the middle ot 

 the river granite veins penetrate the sedimentary rock, whose 

 normal colour becomes lighter in its vicinity. Microscopic 

 sections of the granite obtained at and above this junction 

 show beautiful examples of the micrographic intergrowth of 

 quartz and felspar characteristic of granophyres. At the left 

 side of the photograph, close to the right bank of the river, a 

 dyke of dioritic lamprophyre is seen traversing the Silurian 

 rock in a N.N.W. direction, and is cut off by the granite. The 

 shale in contact is greatly indurated, and so similar in colour 

 to the dyke, that it was not easy to trace the exact line of 

 demarcation. In microscopic section, the intermingling of the 

 green hornblende bands, probably of igneous origin, with the 

 brown clastic patches of the sedimentary rock is very striking.* 

 (Plate 2.) When the river is exceptionally low a continuation 

 of one of the granophyric veins already referred to, can be seen 

 crossing the dyke. 



Donard Tunnel passes close to this junction, and there are 

 large specimens from it on the table — baked sedimentary rock, 

 penetrated by eurite bands. In the course of its construction, 

 I had in September, 1897, an opportunity of seeing dykes of 

 the later series. A very interesting section was then tem- 

 porarily exposed in the '' cut and cover " to this tunnel, about 

 a quarter cf a mile south of the Bloody Bridge River. The 

 normal granite of the district was here seen to about six feet in 

 depth, capped by four feet of drift deposit. Two basalt dykes 

 traversed the granite at an interval of forty yards from each 



* This microscopic section, with one of the dyke itself, was submitted to Professor 

 Cole, to whom I am indebted for the following interesting remarks. "Your 'dioritic 

 lamprophyre ' is a curious rock, with its sparse friclinic felspars, and its groundwork of 

 biotite and green hornblende. It looks as if a magma capable of making biotite 

 and pyroxene had remained as a groundwork after the felspar had developed, 

 and then this magma crystallised out, the pyroxenic matter finally passing into granular 

 amphibole. But the Silurian contact-rock shows similar patches of granular horn- 

 blende, and an abundanee of the same brown mica. Is this rock permeated by the 

 igneous one in intimate streaks, or does the igneous one owe some of its matter to 

 absorption of the adjacent sediment ? The former view looks to me more probable." 



