and Igneous Rocks of Ensay. 115 



felspars and quartz all combined in a holocrystalline structure 

 — the aplites at Ensay are marked by the abraded, fractured, 

 and eroded state of the felspars. Both the orthoclase and 

 plagioclase crystals show these signs of violence, and of long- 

 continued action of the molten, or pasty and still moving, 

 magma. Of the two the potassa felspar has usually been 

 the first formed. 



These appearances accord with my observations that the 

 veins and masses of aplite were forced when in a plastic state 

 into the already metamorphosed sediments. One may in 

 some measure imagine what must have been the pressure 

 and the temperature to which these rocks were then 

 subjected by considering that at that time the locality in 

 question was part of the plane of contact between the 

 Silurian sediments and the invading plutonic masses. 



With the aplites must be classed the pegmatite veins, for 

 their distinction is mainly one of structure. There is, how- 

 ever, this distinction to be noted as regards Ensay : In the 

 pegmatite veins the constituents are much larger individu- 

 ally than in the aplites, but the felspars do not form 

 separate crystals, but are in compound cleavable masses. I 

 have very rarely found any other felspar than an orthoclase 

 or microcline-perthite. In the aplites, however, the mono- 

 clinic potassa and the triclinic soda-lime felspars have most 

 frequently, if not always, been formed independently of each 

 other. 



The massive intrusive rocks of the Ensay district are of 

 the quartz-diorite group. They are massive holocrystalline, 

 and have either a magnesia-iron mica or hornblende, or 

 both together. The samples which I have examined from 

 Ensay do not differ materially from those collected else- 

 where in the district, as, for instance, at NoyaDg. 



The Ensay dykes belong evidently, with the exception of 

 the rarely-occurring basalts, to two classes which correspond 

 to the massive quartz diorites and to the massive diabases 

 of the district respectively. Of the two groups the Diabase 

 dykes are the younger. 



Still more recent are the dykes of basalt, which may 

 probably be referable to the time of the miocene volcanic 

 lava flows of Gippsland. 



I have not thought it necessary to enter into a longer 

 description of the dykes found at Ensay than was necessary 

 to bring them into relation with the other rocks. My 

 principal object has been to work out, so far as I could do, 



i2 



