no SPOLIA ZEYLANICA. 



A brief detscription of the crystalline rocks is now concluded, 

 but a few other points remain to be considered. 



Not a great deal can be said as to the conditions under which 

 the rocks were formed : they must have crystallized under great 

 pressure, and of course the temperature must have been high ; 

 during crj'Stallization the magma was probably rather viscous 

 than fluid. There was evidently much flowing movement. The 

 magma was probably far from homogeneous to begin with, and 

 in addition to this the basic minerals crystallized in general before 

 the acid ; this heterogeneity combined with movement produced 

 the conspicuous mineral banding. Probably the rocks crystallized 

 at a great depth, the absence of even ancient sedimentary rocks 

 overlying the granulites showing that denudation has long been 

 at work in Ceylon. In India as we proceed southwards the 

 palaeozoic rocks die out, and it is probable that the charnockite 

 series is of prepahBOzoic or archean age. 



Since their formation the rocks have suffered from earth 

 movements, but seemingly not of a violent character, inasmuch 

 as there is little evidence of deformation, nor has evidence of the 

 existence of thrust planes or similar phenomena been noted. 



An important series of pressures has thrown the granulites into 

 a main series of anticlinal and synclinal folds, and to this system 

 of folds we may give the name of Taprnhanian ; the axes of the 

 synclines and anticlines, some of which are of great size while 

 others are quite small, have a more or less constant trend about 30° 

 W. of N. in the Kandyan districts, and perhaps more nearly north 

 and south in the Badulla and some other districts ; no evidence to 

 date the movements is available. 



This structural feature of the mountains of Ceylon is rendered 

 conspicuous by its effect on the directions of river systems and 

 even of roads and railways : every one interested in Ceylonese 

 topography must be acquainted with the north-west and south- 

 east valleys which are so conspicuous and which are due to the 

 rivers cutting their way along the foliation planes of the granu- 

 lites, forming strike* valleys, with corresponding strike ridges 

 separating them. Valleys, usually of less importance, have also 

 been made by streams that have cut their way along the joint 

 planes and thus occupy joint valleys oriented approximately at 



* The inclination of a rock to the horizontal is termed its dip ; a line drawn at 

 light angles to the dip on the foliation plane is called the strike of the rock; or 

 the strike might be definited as identical with the outcrop on a horizontal surface. 

 In fig. I the rocks are dipping from left to right ; the water line on the 

 foliation planes serves to indicate the strike. Joints are divisional planes (other 

 than foliation or bedding planes) occurring in a rock, and are usually approxi- 

 mately at right angles to the foliation jilanes. 



