320 On the formation of the 



It occurs in beds in the schistose series; but seldom in 

 association with granite. 



MacCulloch remarks, " that it is only when the base is 

 composed of common (resplendent) felspar, that it resembles 

 granite. 55 This is a matter of course, for as compact felspar is 

 dull and earthy in fracture, it could not be like granite which 

 is crystalline. Dr. Boase makes the difference between green- 

 stone and sienite to consist in the latter containing quartz. 

 This may be, but I cannot define it as a character of the 

 Indian sienite, for it is almost impossible to distinguishbetween 

 resplendent felspar and grains of quartz, when crystallized 

 together in [fine grains. It is sometimes distinctly striped or 

 veined in structure by alternating stripes, or layers of granu- 

 lar hornblende and white felspar; of this kind a beautiful 

 variety occurs at Hoonsoor, west of Seringapatam, where 

 the veined structure is contorted into zigzag waves, not more 

 than two or three inches in length, bent completely back 

 upon the direction like the letter Z. 



Porphyritic Sienite 

 differs from the last only in the crystalline grains of horn- 

 blende being perfectly insulated and separated in a con- 

 tinuous base of felspar, with a dull earthy appearance (proba- 

 bly compact felspar) . This has also a perfect speckled appear- 

 ance, and can therefore be readily distinguished from green- 

 stone. 



Schistose Sienite — Schistose Porphyritic Sienite 

 are only schistose varieties of the two last, the rock having a 

 tabular structure, or is finely laminated into thin plates, some- 

 times not a quarter of an inch thick, or rather it has a tabular 

 cleavage ; for in its mode of aggregation the composing mine- 

 rals do not alternate, so as to cause a striped appearance. 

 These rocks in penological characters differ in no way from 

 the above rocks, except in being schistose. They have gene- 

 rally been included under the varieties of hornblende slate ; 

 but I propose that we should, in India at least, use the above 



