332 



The study of the mode of occurrence, association, and para- 

 genesis of minerals, as well as of their origin and the relations 

 which they bear to the geology of the matrix in which they are 

 imbedded, is one of the highest importance and interest to the 

 mineralogist. It is quite true, however, that the attention of 

 most mineralogists has hitherto been all but exclusively devoted 

 to the study of the crystallographic characters and chemical com- 

 position of mineral species, and has been but little directed to 

 the investigation of the causes which have given rise to the ap- 

 pearances of the minerals themselves ; for this reason, probably, 

 it has become the general custom to regard the presence of most 

 minerals* in rock-masses as merely accidental; and, with the 

 exception of such as are products evidently formed from the alte- 

 ration of other minerals by atmospheric or other sufficiently ap- 

 parent action, few or no attempts have been made either to 

 account for their origin, or to connect their appearance with the 

 grander phenomena of nature which form the subject of geological 

 inquiry. 



The author, however, firmly believing that even the, to our 

 eyes, apparently most insignificant phenomena in nature are never 

 the result of chance, but are invariably due to the operation of 

 definite laws (in many cases at present obscure, but which will 

 ultimately be elucidated by the advances of scientific investiga- 

 tion), could not rest content with the explanation of the presence 

 of such minerals as accidental, and therefore devoted himself to 

 the study of this intricate subject. Although he himself con- 

 siders the results as yet arrived at but very imperfect and in- 

 complete, still he believes them to be so far satisfactory as to 

 justify him in assuming the probability at least of certain general 

 conclusions which these researches have, as it were, forced upon 

 him. 



Excepting only the smaller number of species which make up 

 the bulk of rock-masses in general, it was found upon investiga- 

 tion that most other minerals, when occurring in eruptive rocksf, 

 even when met with in the most widely separated parts of this 



* This term is here employed more especially to indicate such mineral 

 compounds as differ from the bulk of the rock-matrix. 



t The present state of penological nomenclature, already referred to, 

 renders it necessary to define the exact meaning attached to any penolo- 

 gical term used in this communication, in order to. avoid being misunder- 

 stood. By eruptive rocks it is here intended to designate all such rocks 

 as by the naked eye, or, when fine-grained, under the microscope, are seen 

 to possess a true crystallized structure, whilst at the same time, when 

 studied in the field, they are found to intrude into or break through, and 

 send ramifications, dykes or veins, into the neighbouring stratified or un- 

 stratified rock-masses. This term is here used quite independent of any 

 theory (igneous or other) accounting for their origin or formation. 



