200 ON THE GEOLOGY AND PETROGRAPHY OF BATHURST, N.S.W., 



In weathering, the granite gives rise to a rather poor and barren 

 soil. Fortunately, soils resulting from either granites or sand- 

 stones are seldom found alone. Everywhere there is spread about 

 a certain amount of alluvium from the old river beds. And over 

 large tracts traces of a rich soil, resulting from the decomposition 

 of basalts, can be detected. 



Origin of the Granite. — There is a growing belief in the meta- 

 morphic origin of many granites. The Bathurst granite, being 

 limited in extent and easily accessible to its boundaries, presented 

 special facilities to study its origin. It is now a common position 

 for geologists to hold that, although in many and perhaps most 

 instances, granite is an intrusive rock of plutonic origin, yet 

 granites do occur which are the result of extreme metamorphism. 

 Examples are eagerly sought for to show that granite can be pro- 

 duced by the metamorphism of sedimentary materials in situ. 



At the very outset I may state that although I am tolerably 

 familiar with the line of junction between the slates and granites, 

 I have never met with one instance of a gradual change by which 

 granite could be said to melt away on all sides into the surrounding 

 strata, or in which an undoubted granite shades off, by gradations, 

 into a rock of clastic origin. In studying the origin of the granite, 

 the boundaries and junction lines will naturally afford interesting 

 material. Are these boundaries marked by a hard and fast line 1 

 Does the granite mass behave like an eruptive rock 1 Does it 

 alter the rocks it touches ? Does it thrust dykes and veins into 

 the rocks around, or do the many square miles of granite melt 

 away, by insensible gradations, into slates and phyllites ? 



Wherever I have observed contacts, the line of junction has 

 been hard and fast. The granite does thrust out veins into the 

 slates near it, and, without doubt, it alters clay slates to hornfels. 

 The granite is, therefore, in a sense intrusive, but this does not 

 exclude the view that it may have been, for all that, derived from 

 pre-existing sediments. I will now describe a few instances that 

 will maintain my position as to the intrusive nature of the granite, 

 and then consider the probabilities of its being derived from pre- 

 existing seclimentaries. 



