620 Mr. J. Beete Jdkes and the Rev. Samuel Haughton on the 



Description of the foregoing Greenstones. 



No, 1. West Aston; dark greenish-gray rock, with glancing surfaces of bronze mica, and 

 alternating parallel faces of felspar of high lustre. It is composed of — 



(a) Felspar, pale greenish; translucent, with \ in. irregular shining faces, 



giving a remarkable aspect to the rock. 

 (6) Bronze mica, faces sometimes J in. by -J in. ; presenting the same glancing 

 effect as the crystals of felspar. 

 No hornblende of any kind visible; the felspar predominates, but the thin flakes of 

 bronze mica are very conspicuous. 

 No. 2. West Aston; fine-grained crystalline greenstone, into which the rock No. 1 probably 

 passes. It is composed of — 



(a) Felspar, white, with occasionally a pale greenish tinge; semi-opaque. 

 (6) Mica, rarely white; in minute flakes, passing into a greenish amorphous 

 mineral, apparently in equal quantity with the granular white felspar. It 

 is a leaden-coloured greenish mica, not either hornblende or chlorite. 



An inspection of the foregoing analyses is sufficient to prove that these rocks 

 belong to the basic group of igneous rocks. In the absence of all information 

 as to the chemical composition of the separate minerals composing them, it 

 would be impossible to interjiret the analyses so as to deduce from them the 

 mineralogical composition of the rocks. 



Two different hypotheses may be made respecting these rocks : — 



1st. They may be regarded as proceeding from a different molten rock 

 mass from that which produced the granites and felstones of the district. In 

 this case their chemical composition is an ultimate fact, and there is nothing 

 more to be said respecting it. 



2nd. They may be regarded as metamorphosed granite, i. e. granite con- 

 verted into syenitic greenstone by the addition of bases which acted as fluxes. 

 If we knew the bases that were added, or their relation to each other, we should 

 be able to effect the solution of equations similar to (22), established for the 

 Coollattin granite. In the absence of this knowledge, we are driven to use pro- 

 bable hypotheses. 



I have already considered two hypothesis (A) and (B), both of which are 

 rendered extremely doubtful from our ignorance of the precise nature of the 

 rock that was added to the molten granite. On the present occasion I shall use 

 a third hypothesis, which is perhaps as improbable as either (A) or (B), but 

 which will serve to bring out prominently the real differences between the gra- 

 nites of the main chain and the greenstones associated with the felspathic traps. 



