118 The Sedimentary, Metamorphic, 



It is to the close of the Silurian, or to the commencement 

 of the Devonian, age that for the present I refer the 

 igneous and metamorphic rocks of Ensay. 



It remains now for me to consider what may have been 

 the sequence in which the present relations of the Ensay 

 Rocks have been brought about. 



Although the sediments on the western side of the Tambo 

 River are not continuous with the schists at Ensay, yet an 

 examination of both groups in situ, and of samples in thin 

 slices under the microscope, leaves no doubt in my mind 

 that the latter are the very much metamorphosed forms of 

 sediments which represented the latter. The schistose rocks 

 of Contentment Hill, some of the very fine-grained mica 

 schists at the Little River, and the altered sediments whose 

 traces now only remain at the sources of Watts Creek, supply 

 intermediate stages connecting the extreme examples. With 

 these exceptions, the sedimentary rocks have been com- 

 pletely denuded on the eastern side of the Tambo River 

 from the country crossed by the section. 



The most interesting part of the locality, and the one to 

 which I have desired to direct attention, is that at the junc- 

 tion of Watts Creek and the Little River. It is there that 

 the schists have been preserved from denudation, either 

 by having formed a depression below the general plane of 

 contact, or by having been let down by faults. It is im- 

 material which may be the true explanation. That which 

 is material is the very instructive manner in which the 

 schistose and igneous rocks are associated. At first sight it 

 seems that they are in complete confusion, but on further 

 examination this seeming disorder is capable of explanation. 

 It is to be borne in mind that this locality is, as I have 

 before said, part of the plane of contact between the sedi- 

 ments and the invasive igneous rocks. Taking a general 

 view of the whole of the Australian Alps, I find that this 

 plane of contact is a most irregular one. Its highest and 

 lowest limits are beyond an accurate determination, for to 

 estimate them it would be necessary to have a knowledge of 

 the faults which have disturbed the continuity of the con- 

 tact plane, of the probable thickness of the sediments where 

 the contact is deep below the surface, and of the amount 

 denuded from the highest points of the now protruding 

 plutonic masses. The Ensay district is a good example of 

 the difficulties in the way of such a determination. The 

 Silurian beds at the west side of the Tambo River are at its 



