Notes on the Area of Intrusive Rocks at Bar go. 135 



but that there may have been also an accession of it from 

 elsewhere^ and also that in the neighbourhood of the 

 intrusive rocks there may have been to some extent an 

 impregnation by them of the metamorphosed beds with 

 portions of their own materials. 



In addition to the heat due to the proximity of the 

 plutonic rocks, to the pressure due to the depth below the 

 earth's surface at which this contact action took place, to 

 the action of the mineralised waters included in the sedi- 

 ments, and of the additional water set free during their 

 molecular alteration, account must be taken of the effect of 

 vast mechanical stresses and movements to which the strata 

 bear witness. 



The normal strike of the Silurian strata of the district 

 may be taken as about N. 30 degs. to 40 degs. W. At 

 Dargo, for instance at Orr's Creek, I have found the strike 

 of the metamorphosed strata east and west. It is not an 

 isolated case, but occurs in other places — for instance, at 

 Swift's Creek, on a large scale — and it seems probable that 

 this extensive diversion of the strata has been due to the 

 violent forcing of the igneous masses when in a plastic 

 condition into the opening sedimentary beds during eleva- 

 tion of the earth's crust. 



The Intrusive Rocks. 



Aplites. — I have found it necessary to use the word aplite 

 for a certain class of intrusive dykes and veins which I have 

 found in places at or near to the contact, and which are 

 very near in character to certain dykes and masses of igneous 

 rock at Ensay and Omeo, to which I have applied that 

 name. The word aplite is, however, not quite satisfactory 

 if it is restricted to rocks comino- under the definition 

 " Muscovite Granites." Although in the cases to Avhich I 

 now refer the generality have muscovite mica in small 

 amount, there are some which have traces also of biotite, or 

 a small amount of biotite only. However, with this proviso 

 I use the term aplite in this paper.* 



Where the contacts can be examined, as at Orr's Creek, 

 dykes and veins are found to cross them at various angles. 

 They have all the main characteristics of aplite — namely, 

 that they are crystalline-granular compounds of felspars and 



* See Eosenbusch Physiographie der Massigen Gesteine, p. 19 ; also 

 Die Steiger Schiefer, p. 277. 



