197 



The bulk analysis shows that the rock is closely allied to the augite- 

 andesites in composition. It is interesting to compare the kernels of glass 

 with the bulk analysis. They contain more silica ; less lime, iron and 

 magnesia ; and doubtless more alkali, although this point was not deter- 

 mined. They represent the acid residuum left after a certain amount of 

 crystal development had taken place (see ante p. 43). 



The Eskdale dyke, which, it must be remembered, presents the 

 remarkable characters above described only in one portion of its course, 

 has been traced from the Lead Hills in Lanarkshire to Liddlesdale (a 

 distance of 45 miles), and for some miles further into England. 



At Craighead, near Crawfordjohn, Lanarkshire, there occurs a very 

 remarkable rock. It appears to be an abnormal variety of one of the N. W. 

 and S.E. (Tertiary) dykes. It would have been described by the older 

 petrographers as an augite-porphyry. Macroscopically, it consists of a 

 large number of very perfect augite-crystals, often measuring 7 or 8 

 mm. in length, by 4 or 5 in breadth, lying in a greyish crystalline ground- 

 mass. Under the microscope the augite is seen to be deeply coloured. 

 It contains lath-shaped felspar and olivine as inclusions, and the felspars 

 are arranged with their long axis parallel with the external faces of the 

 augite. The ground-mass is composed of lath-shaped plagioclase, olivine, mag- 

 netite and a certain amount of interstitial matter. Apatite is very abundant. 

 The olivines are very fresh and distinctly coloured. Magnetite has been 

 deposited along the cracks, and this has taken place without the develop- 

 ment of any trace of alteration in the olivine itself. The interstitial 

 matter and the felspars appear to have been more or less affected by altera- 

 tion ; but no evidence of the development of analcime, as in the Car Craig 

 rock, has been detected. 



The Southern Uplands of Scotland are bordered on the south by 

 a fringe of Lower Carboniferous rocks with which are associated con- 

 temporaneous volcanic products. These have not yet received detailed 

 examination, but they belong in all probability, for the most part, to the 

 intermediate series. They may be followed almost continuously from near 

 Dunse, in Berwickshire, by Kelso, Ruberslaw, Langholm, Birrenswark, and 

 the Annan to the mouth of the Nith, at the foot of Criffel. At Stickhill, 

 north of Kelso, there occurs in this series a porphyritic olivine-basalt 

 bearing many points of resememblance to the rocks near Arthur's Seat. 

 It consists of good sized crystals of bytownite, augite, and olivine in a 

 ground-mass essentially composed of rather short lath-shaped felspars 

 (labradorite ? ), granules of augite and magnetite/ 1 ) 



Highlands of Scotland. Basic igneous rocks, essentially composed of 

 plagioclase and pyroxene, are found associated with the gneisses and schists 

 of this region. They have not as yet received much attention at the hands 

 of petrographers. A dyke occurring in the Hebridean gneissic system of 

 Sutherlandshire, near the village of Scourie, has been examined by the author 

 of the present work, and has been already referred to as illustrating the 



(1) TEALL. G. M., Decade II., Vol X., 1883, p. 252. 



