from the Standpoint of Physical Chemistry. 231 



All stages of resorption appear in different parts of this 

 slide. An example is sketched in fig. 11. Without the analy- 

 zer the corroded forms shown in heavy lines in the sketch 

 (now replaced by calcite) are all that appear, but with crossed 

 nicols the crystal form, almost complete, is brought out in 

 serpentine. Immediately adjacent are remnants of several 

 other crystals which the crossed nicols similarly outline. 



In fig. 12 the typical manner in which oxide of iron has 

 separated along cleavage cracks of the original mineral is 

 shown, although nothing but alteration products survive. The 

 resemblance to olivine is obvious. 



From such examples one may pass by gradual transition to 

 the results of almost complete resorption, in which the rounded 

 and blurred outlines convey only a vague suggestion of the 

 original form of the crystal, and upon whose areas, spreading 

 out into the glass, microlites are encroaching. The color in 

 such cases is practically the same as that of the surrounding 

 glass, but crossed nicols show the presence of aggregates of 

 minute chlorite scales. 



The stages of the process and the relations which the olivines 

 bear to the plagioclase and diopside are sketched in fig. 13. 

 Similar phenomena are shown in slide No. 83, in No. 30, 

 and in No. 48. In No. 57 the several steps can be followed 

 very perfectly. 



Fig. 13. 



Fig. IB. Breaking-up and resorption of olivine. Several stages, found 

 in various portions of the slide, are brought together. (Slide No. 105.) 

 Diameter of field V5 mm . 



In No. 54 the outline of an original olivine crystal is pre- 

 served, but most of the area within the boundary of the 

 original crystal is occupied by a mixture of brown glass and 

 irregular grains of a dark brown color. This form of attack 

 upon the olivine, by which the crystal has been broken up 

 into many fragments, appears to have been common, and the 

 brown grains show up in many of the slides, at times associated 



