182 REV. J. MILNE CURRAN. 



often resorted to this test, and at the same time noticed the effect 

 on any secondary products in the same slice. Basic glasses are 

 frequently more soluable than acidic ones.* 



Besides examining the rocks in thin slices, I have made notes 

 on the appearance the rock presents as it is reduced by grinding 

 from an opaque to a translucent chip, and finally to a transparent 

 section. Occasionally I have separated the more magnetic minerals 

 by an electro-magnet for separate examination. 



Except using the blowpipe to test the fusibility of such rocks 

 as basalt-glasses, the foregoing are the only methods resorted to 

 in preparing this paper. 



I have, however, largely availed myself of notes made in the 

 field when collecting my samples. Occasionally one must deal 

 with rocks of whose relations in the field nothing is known. The 

 writer believes that this places any observer at a great disadvan- 

 tage, and even in experienced hands is fruitful of error. The 

 mode of occurrence of a rock in the field is a factor that should 

 never be overlooked in microscopic study. 



The macroscopic character of rocks is of much assistance in 

 reading the microscopic structures of rock-slices. For this reason 

 chips of all the rocks are preserved and submitted with this paper. 



Previous Observers. 

 The following papers have references, more or less copious, to 

 the Microscopic Structure of Australian Rocks. I found the list 

 useful and insert it here for the convenience of my readers. 



1872. Daintree, R. — Notes on the Geology of Queensland — Quart. 

 Journ. Geol. Soc, Yol. xxviii. p. 271. This paper contains 

 some notes by Mr. Alport on some diorites, trachytes, por- 

 phyrites and dolerites from Queensland. There are three 

 plates showing the micro-structure of these rocks. 



1875. Daintree, R. — Notes on the Microscopic Structures of cer- 

 tain Igneous Rocks, submitted by the Director of the Geo- 



* Professor Judd and Mr. C. G. Cole on the Basalt Glasses of Western 

 Scotland— Quart. Journ. Geol. Soc v Vol. xxxix., p. 453. 



