288 J. S. Diller — Mica-peridotite from Kentucky. 



transparent. The crystals vary in size from -01 mm to 'l mm in 

 diameter and are almost always black-bordered. The chemi- 

 cal analysis of the rock shows that it contains 3*78 per cent 

 Ti0 2 with 9 - 46 per cent CaO. After taking out of the analysis 

 the elements demanded for the other determined minerals 

 there yet remains essentially the composition of perofskite. 

 Titanic acid is frequently found in biotite and it is desirable 

 that analyses be made of both biotite and perofskite in this 

 case ; but as the minute crystals of perofskite are generally en- 

 veloped by the biotite it would be very difficult and perhaps 

 impossible to satisfactorily separate them. 



The muscovite, chlorite, magnetite, apatite and fibrous cal- 

 cite have no features deserving special mention. The brown- 

 ish gray clouded material which is next in abundance to the 

 serpentine is scattered throughout the section generally between 

 the scales of biotite, but often within them. It is without 

 crystallographic outline or such physical features as definitely 

 indicate its origin. 



The following chemical analysis of the rock for which I am 

 greatly indebted to Mr. W. F. Hillebrand was made in the 

 chemical laboratory of the U. S. Geological Survey. 



SiO„ 33-S4 



TiO„ 3-78 



AL0 3 5-88 



Cr o 3 0-18 



Fe 2 3 .__ 7-04 



FeO . 5-16 



MnO - 0-16 



NiO 0-10 



CoO tr. 



CaO 9-46 



BaO 0-06 



MgO 22-96 



K„0 2-04 



Na 2 0-33 



H„G 7-50 



P o "0 0-89 



CI / 0-05 



Fl --J ? 



CO„ 0-43 



99-86 



In addition to the water given, the sample lost 0"68 per cent 

 water at 100° C. The large percentage of H 2 and C0 2 shows 

 the highly altered condition of the rock. 



Among the peridotites already described Kosenbuseh has 

 recognized six forms. Considering only their essential constit- 



