STRUCTURAL AND FIELD 
GEOLOGY 
CHAPTER I 
ROCK-FORMING MINERALS 
Oxides—Quartz and its varieties; Opal; Specular Iron; Ilmenite; 
Magnetite ; Limonite; Rutile; Zircon; Spinelloids ; Corundum ; 
Pyrolusite, Psilomelane, and Wad. Silicates—Felspar Group ; Fels- 
pathoid Group. 
BEFORE the phenomena presented by the framework of the 
earth’s crust can be fully appreciated, one ought to have 
some knowledge of rocks and their various constituents. 
This is all-important for the student who is specialising in 
geology. For others who wish merely to obtain such aid in 
their several occupations as this science can supply, a more 
moderate acquaintance with minerals and rocks than the 
seologist requires may suffice, and it is for this class of 
students more especially that the following descriptions have 
been written. In these introductory chapters, therefore, 
special attention is paid to macroscopic or megascopic char- 
acters—those, namely, which may be observed in hand- 
specimens, with or without the help of a pocket-lens. As it 
is hoped, however, that some readers may be sufficiently 
interested to wish to know more, a few notes in smaller type 
have been added, giving further details and describing char- 
acters which can only be studied in thin slices under the 
microscope. It is quite a mistake to suppose that any great 
knowledge of mineralogy is required to enable one to deter- 
mine the essential ingredients of a fine-grained rock in this 
way. With ordinary application one may in a short time 
A 

