262 THE CEYSTAL FALLS lEON-BBARING DISTRICT. 



AGE OF PERIDOTITES. 



The only stateiueut which can be made concerning the age of the peri- 

 dotite dikes is that they are younger than some of the gabbros, and that, ' 

 not having suffered the deformation of the pre-Keweenawan orogenic move- 

 ments, they are Keweenawan or post-Keweenawan. 



GENERATE OBSERVATIONS ON THE ABOVE SERIES. 



TEXTURAL CHARACTERS OF THE SERIES. 



There are represented in the above series rocks with moderately fine 

 grain as well as those of very coarse grain. They vary from those with 

 parallel texture, through those with porphyritic, poikilitic, and ophitic texture, 

 to those with granular texture. There is, however, tlu'oughout a clear 

 preponderance of the medium to coarse granular rocks. The rocks are 

 evidently not of effusive character, though some possess the textures prev- 

 alent in effusive rocks. 



The order of crystallization of the minerals in the rocks of granular 

 texture, excluding the iron ores and the accessory minerals, is as follows. 

 The order in the imperfectly ophitic and porphyritic rocks is not considered, 

 as those are rather exceptional occurrences. 



In the lists those minerals are hyphenated of which it has not been 

 possible to determine accurately the order of crystallization. It seems that 

 either they were formed at the same time or, in some cases, their formation 

 has overlapped. In such cases the one placed first is the one presumed to 

 have begun its crystallization first. 



DiORITE. GaBBRO and HORN- BRONZITE-NORITE. PeRIDOTITE. 



BLENDB-GABBRO . 



Hornblende. Olivine. Bronzite. Olivine. 



Biotite. Monoclinic pyroxene. Monocliuic pyroxene. Ortliorbombic pyroxene. 



Plagioclase. Biotite-bornblende. Biotite-bornblende. Monoclinic pyroxene. 



Microcline. Plagioclase. Plagioclase. Biotite-hornblende. 



Ortboclase-quartz. Plagioclase. 



For the entire series the order may be arranged as follows: Olivine, 

 bronzile, monoclinic pyroxene, mica-hornblende, plagioclase, orthoclase, 

 quartz. This is the same order that is exhibited by the most basic rock 

 represented in the series, the peridotite, so far as this rock contains the 

 minerals. 



