Researches in British Mineralogy. 223 



secution of petrological investigations. Speculations are made on the 

 cliemical changes which our rock-masses have undergone before we 

 are in possession of accurate data respecting the mineralogical cha- 

 racter and chemical composition of the rocks themselves. " Only very- 

 few chemical analyses of British rocks have been made," and it is 

 humiliating to learn that, " in this respect, England stands far be- 

 hind the rest of Europe ; France, Germany, Russia, and even the 

 small kingdoms of Norway and Sweden are far in advance with 

 regard to the knowledge of the chemical and mineralogical compo- 

 sition of their rocks." Through the absence of exact information on 

 this important subject, the nomenclature at present used by petrolo- 

 gists " is altogether inadequate to the demands of the more advanced 

 state of the other branches of geological inquiry ; in geological sur- 

 veys and maps it is common to find eruptive rocks of totally different 

 mineral and chemical composition and age confounded with one 

 another, and, in other cases, to find rocks coloured and described by 

 names that do not pertain to them. In fact, the present state of 

 classification and nomenclature of the eruptive rocks is such that it 

 becomes impossible to know with any certainty what exact rock may 

 be intended or mapped under the names generally in use." The 

 science of mineralogy, as expounded in text books, is too apt to be 

 considered merely to treat of the physical, chemical, and crystal- 

 lographic characters of mineral species, and to end here. "The 

 study of their mode of occurrence, association, and paragenesis, as 

 well as of their origin and the relations which they bear to the geo- 

 logy of the matrix in which they are embedded, is one of the highest 

 importance and interest to the mineralogist." These considerations are 

 generally neglected, and it has become customary to regard the presence 

 of minerals in rock masses as accidental, and to shirk the question of 

 their origin. It is evident, however, their presence is due, not to 

 chance, but to the operation of definite laws ; and to this important 

 subject the author directed his attention. His researches have led 

 him to certain general conclusions, which are given. " Excepting 

 only the smaller number of species which make up the bulk of rock 

 masses in general, it was found that most other minerals when oc- 

 curring in eruptive rocks, even when met with in the most widely 

 separated parts of the globe, present themselves under similar con- 

 ditions, have the same associated minerals along with them ; and 

 that the eruptive rocks in which they occur, whenever the age of 

 their intrusion could be satisfactorily ascertained, frequently, if not 

 always, corresponded in geological chronology." In the eruptive 

 rocks by far the greater number of mineral species have been found ; 

 and in all parts of the globe the same or very analogous minerals 

 are, as a rule, found to accompany the outbursts of similar eruptive 

 rocks. Far, therefore, from regarding the appearance of minerals in 

 eruptive rock-masses as accidental or extraneous, the author holds 

 that more extended and accurate investigation will demonstrate, that, 

 in like manner as the occurrence of certain fossils or groups of 

 fossils enables the geological age of a sedimentary bed to be deduced, 

 so will the presence of certain minerals, or classes of minerals, serve 



