

132 HOLLAND : GEOLOGY OF THE NEIGHBOURHOOD OF SALEM. 



and plates, after the style of schillerized felspars, whilst there is 

 a greater development of secondary green hornblende at the 

 expense of the pyroxene than is usual in these dykes. As all 

 the rocks in the neighbourhood of the Chalk hills, includ- 

 ing the Shevaroy mass, are schillerized, and as the phenomena of 

 schilierization are generally held to be due to secondary causes, 

 these points of difference between the Karipatti dyke and those 

 further west are of no importance. But one point remains, how- 

 ever, unexplained, namely, the brown colour of the felspars in the 

 Karipatti dyke which is the usual thing in these rocks, and the 

 clear colourless character of the felspars in the other two dykes 

 which is an unusual character. Personally, I am inclined to regard this 

 brown dust in the felspar as original, whilst the rods and plates 

 constituting the schiller phenomena are secondary, and manufac- 

 tured by secretion and subsequent deposition of the compounds of 

 the brown dust along planes of chemical weakness. For this 

 assertion the evidence is not yet sufficiently clear to ^constitute any- 

 thing approaching proof, and the point should therefore be kept in 

 abeyance. But with the exception of this one point, whose meaning 

 is doubtful, the three dyke exposures near Salem belong essentially 

 to the same rock, and almost certainly are the result of the same 

 eruption. But whether or not the three detached exposures were origi- 

 nally irrupted into the same fissure, is an important question which is 

 less easy to decide. If we could but settle this point, we should have a 

 simple guide as to the nature and amount of disturbance which has 

 taken place in this area since the formation of the dykes {vide page 



39)- 



Besides the large dykes measuring some 50 yards wide, nar- 



Narrow subsidiary apo- row apophyses run out into the surrounding 



physes. rocks, and often continue for some distance 



approximately parallel to the large dyke. The composition of these 



narrow dykes is essentially that of the large ones, but they show 



( 30 ) 



