GENERAL GEOLOGY 41 



ferred to the Carboniferous. It may have been derived 

 from just such a series of rocks as the Vancouver Series, 

 and it is associated with the same granitoid eruptives which 

 accompany the Vancouver Series along the Alaska coast. 



IGNEOUS ROCKS 



(n) Hornblende-blotite-tonalite (372), identical with a boulder 

 from Plover Bay described below. 



Hornblende-biotite-tonalite (205), nearly identical with the above 

 but showing many perfect amber-colored titanites just visible to the 

 eye. This is represented in the collection by several varieties. 



(0) Normal, rather coarse grained, biotite-hornblende-granite with 

 abundant porphyritic Carlsbad twins of orthoclase. 



(/) Dark grey medium-grained granite, with much more biotite 

 than the other forms. 



(^) Aplite. A very compact, almost aphanitic, pearl grey pebble ; 

 agrees almost exactly with the aplite from St. Matthew Island. 



(r) Porphyritic liparite perlite (218} . White feldspar crystals 

 appear abundantly in a brick-red base of pitchstone. 



The microscope (plate iv) shows a blood-red glass, affected every- 

 where by a perfect perlitic structure. The glass shades into deep red- 

 brown spots or into pale red areas. The perlitic centers are often 

 occupied by oil -green amorphous-appearing areas of microfelsite, which 

 polarize fibrous and negative. This is also developed into minute 

 spherulites, which are partly enclosed in the feldspar, and are broken 

 and moved apart. The original fissures are now represented by broad 

 bands which are colorless and granularly devitrified. The biotite is 

 twisted and largely decomposed by fusion, with separation of black ore. 

 The feldspars are often broken. The rock is an oligoclase-albite-bear- 

 ing perlite. It represents the first step the embryonic form in the 

 development of lithophysae, in accord with the explanation of the proc- 

 ess given by Professor Iddings. The separation of water at these 

 points has caused the development of compounds having a green color, 

 as is common in lithophysa?, and has caused disturbances there the 

 cracking of the spherulites, and polarization, while the glass around is 

 unstrained and unaltered. 



(5) Augite-orthophyr (207) . A chocolate, felsitic base, with small 

 flesh-colored feldspars and red biotite. The feldspars and the green 

 augites are wholly decomposed under the microscope. 



