224 HOLLAND: CHARNOCKITE SERIES. 



black bands were found to bifurcate and so form two distinct 

 bands. Both instances are shown in plate IX. Although there is 

 no question about the fact that the hornblende rock is a distinct injec- 

 tion along the foliation planes of the gneiss, it never shows a chilled 

 selvage ; but on the contrary its crystals, though slightly coarser in 

 grain than the otherwise similar hornblende of the gneiss, interlock 

 across the junction after the manner of the schlieren already des- 

 cribed. The hornblende bands and hornblendic gneiss which they 

 traverse are, from the character of their constituents, clearly relatives 

 and derived from the same magma, and the former must have been 

 injected whilst the latter was still hot. A somewhat similar relation 

 between the pyroxenite and norite has been observed at Pallavaram 

 and elsewhere; but the Tirrupur case is quite the most striking in- 

 stance I have seen showing that banding maybe produced by succes- 

 sive injection of slightly different, but genetically related, rocks. 



(b) Apophyses and Dykes. 

 As a general rule attempts to recognise apophyses and dykes 

 proceeding from any large massive constituent 



Destruction of evidence. ■ . .... , ... 



of the crystalline schists will be attended with 

 failure, for the very good reason that any dykes or veins originally 

 existing will generally be squeezed out to form apparently inde- 

 pendent parallel bands or lenticular masses without determinable 

 connection with the main formation. The deformation of a series of 

 radiating veins by pressure exerted in a direction at right angles to 

 the general foliation will thus increase the resemblance to the 

 common banding cf gneisses. Moreover, there is a natural tendency 

 for an intrusive rock to follow the cleavage and foliation planes, 

 which is the direction of least resistance {vide supra, p. 223 and plate 

 IX). 



Fortunately the charnockite series appeared in South India 

 after the close of the most severe earth-movements, and the original 

 vein and dyke structures have not been wholly obliterated by the 

 subsequent, feebler dynamo-metamorphism. 

 ( 106 ) 



