JOURNAL 
OF TIIE 
gtirrostapical Sncictn af ^itinrui. 
Notes on the Microscopic Structure of some Igneous Dykes of North 
Gippstand. By A. W. Howitt, F.G.S. 
[With Plate.] 
[Read 25tli Nov. 1875.] 
In studying the petrology of North Gippsland many interesting 
lines of inquiry present themselves, as to the three great classes of 
rock formations, the sedimentary, the igneous, and the rneta- 
morphic. The questions to be asked arrange themselves under 
various heads, and of these, one includes those which relate to the 
mineral constitution, the genetic relations and the classificatory 
position of the intrusive dykes. 
In petrology, as in many other branches of science, the micro¬ 
scope has become a powerful instrument of research. The methods 
of inquiry have been most admirably worked out, both in England 
and on the continent of Europe. It is owing to the labours of 
Rosenbusch, Sorby, Allport, Zirkel, Streng, and others that 
micropetrography has almost assumed the dimensions of a separate 
branch of science. * 
The notes which I propose to lay before this Society are the 
result of my investigations as to one group of igneous dykes in 
North Gippsland, and will, I hope, prove to be of interest to 
microscopists as well as to geologists. 
Geology of the Locality. —The locality in which these dykes are 
found is situated on the road from Sale and jBairnsdale to Dargo. 
It commences at Cobbannah Creek and continues along the road 
nearly to Squirrel Forest. 
* The works of Professor Rosenbusch on the Microscopic “Physiography ” 
of Minerals and of Rocks, are pre-eminent by their thorough mastery of the 
subject, and the wido field they cover. 
Yol. 1. No. 4. 
p 
