No. 4.] HARRINGTON — CANADIAN .MINERALS. 249 



given by Gu:»tav Rose to crystals possessing the form of pyroxene 

 but cleavage and other characters of hornblende, and first ob- 

 served by him in certain rocks from the Urals, which he termed 

 uralite porphyrias. The larger crystals were found to frequently 

 contain a kernel of pyroxene, which in the smaller ones had en- 

 tirely disappeared. In the case of pyroxene from Arendal in 

 Norway also, Rose observed a perfect transition from lustrous 

 crystals showing no apparent trace of hornblende within to others 

 with drusy surfaces, in which no trace of augite could be de- 

 tected. ''"^ 



Crystals of pyroxene from Traversella afford another example 

 of a change of this kind. The unaltered crystals are described 

 as transparent and glassy, but on being altered become opaque, 

 and often assume a silky lustre. In this opaque portion fine 

 fibres running parallel to the principal axis begin to be developed, 

 and, as the change advances, distinctly recognizable individuals 

 of hornblende are formed, also parallel to the principal axis and 

 looking like actinolite.f 



Of late years, by the aid of the microscope, it has been de- 

 monstrated that the development of uralite has taken place in 

 many crystalline rocks, not only in Europe but on this side of 

 the Atlantic- In the case of diabase, the change of this kind 

 has been described by Rosenbusch as follows: J — " The altera- 

 tion processes to which the augite of diabase is subject is one of 

 most varied character. Ordinarily, they begin with the forma- 

 tion of a vertical fibrous structure. At the same time the fibres 

 often take the form of well-defined uralite, and in this case the 

 process commonly begins from the entire periphery of the augite, 

 and proceeds thence towards the centre, in general more rapidly 

 in the direction of the vertical axis than at ri^ht ano-les to it. 

 So long, then, as the process is not wholly completed, there re- 

 main in the interior portions of augite with irregular outline. 

 Less frequently, or rather only in exceptional cases, the formation 

 of uralite does not begin along the whole circumference, but 

 attacks only single narrow strips in a vertical direction, so that 

 thin columns of augite and uralite, parallel to the vertical axis, 

 alternate with one another. The uralite itself passes, on still fur- 



* Bischof, Lehrbiich der Geoloyic. 1864, \)\). 023, 624. 



t Lehrbuch der Geologic^ Bischoff, 1851, p. o39. 



\ MikroskoiJ, Phy^iogr. d. massigen Gesteine. 1877. p. .330. 



