1864.] T. STERRY HUNT ON LITHOLOQY. 21 



indigenous rocks, or sediments altered in situ, and exotic rocks, or 

 sediments displaced and translated, forming eruptive and intrusive 

 masses. Under the head of exotic rocks is however to be included 

 another class of crystalline aggregates, which are for the most 

 part distinguished by their structure from injected or intrusive 

 masses. I refer to the accumulations which fill mineral veins, and 

 which doubtless have been deposited from aqueous solutions. 

 "While their peculiar arrangement, with the predominance of 

 quartz and non-silicated species, generally serves to distinguish 

 the contents of these veins from those of injected plutonic rocks, 

 there are not wanting cases in which the predominance of feld- 

 spar and mica gives rise to aggregates which have a certain 

 resemblance to dykes of intrusive granite. From these however^ 

 true veins are generally distinguished by the presence of miner- 

 als containing boron, fluorine, phosphorus, coesium, rubidium, lith- 

 ium, glucinum, zirconium, tin, columbium, .etc. ; elements which 

 are rare, or found only in minute quantities in the great mass of 

 sediments, but are here accumulated by deposition from waters, 

 which have removed these elements from the sedimentary rocks, 

 and deposited them subsequently in fissures. 



No one at the present day will probably be found to deny the 

 plutonic origin of most non-stratified rocks, so that the once vexed 

 questions of the neptunists and plutonists may be regarded as set- 

 tled. If however we go back but a few years in the history of 

 geology, it will be foand that an eruptive origin was then claimed 

 for many rocks which are now admitted to be indigenous. It is 

 scarcely necessary to refer to the views of those who have main- 

 tained the exotic character of many quartzites and crystalline 

 limestones, when a majority of writers, even to the present day, 

 class serpentines, euphotides, and hyperites among eruptive rocks ; 

 although the experience of every field-geologist is accumulating, 

 from year to year, a great mass of evidence in favor of the indige- 

 nous nature of all these rocks. The sedimentary and indige. 

 nous character of very many granites, syenites, and diorites will 

 now no longer be questioned. Thus we find, for example, that 

 the melap'jyres of the Tyrol, which, in Von Buch's too-famous 

 theory ot doloraitization, were supposed to have been erupted to- 

 gether with magnesian vapors which eff'ected the alteration of 

 the adjacent limestones, have been shown by Fournet to be sedi- 

 ments of Carboniferous age, metamorphosed in situ, — indigenous 



