CONTACT METAMOEPHISM BY INTRUSIVES. 



207 



Differing slightly from the ordinary spilosite is one in which the spots 

 ^re of microscopical size, and consist of ragged bunches of chlorite and aggre- 

 .-gates of sphene and epidote, with some flakes of biotite, which lie in a quartz- 

 feldspar mass. The photomicrograph, fig. B of PI. XXXVII, illustrates the 

 appearance of the rock. As these spots increase in luimber they approach each 

 other and unite, forming streamers, which in their turn unite and form bands 

 (photomicrograph, fig. A, PI. XXXVIII,). The spilosites or spotted contact 

 products thus pass over into the desmosites or banded contact products. 



Analyses of spilosites. — Aualyses of two of tlic spilositcs (Nos. I and II) were 

 made by Dr. H. N. Stokes in the laboratory of the United States Geolog- 

 ical Survey, and are here appended. With them there is given an analysis 

 ■{No. Ill) by E. Kayser of a spilosite from the Harz Mountains 



Analyses of spilosites. 



SiO.2 



TiOi 



Al^Oj 



Cr.O., 



Fe,03 



FeO 



MnO 



CaO 



BaO 



SrO 



MgO 



Na.O 



KjO 



LioO 



C0.2 



PiOr, 



H.OatllO^... 

 H.2O at 110^ + 

 Sand SO:, ...- 



CI 



F 



Total .. 



57.77 



.92 



19.35 



None. 



1.29 



3.37 



Trace. 



1.71 



None. 



Trace. 



4. 3.'. 



8.22 



. 22 



Koiie. 



Noue. 



.04 



.18 



2.34 



None. 



Noue. 



None. 



52.51 



1.70 



19.00 



None. 



3.31 



7.19 



Trace. 



1. 55 



Trace. 



Trace. 



3.29 



6.72 



.70 



Trace. 



None. 



.15 



.34 



3.26 



None. 



None. 



Trace. 



18.15 



5.08 



7.04 



.51 



1.40 



3.17 

 4.20 

 2.25 



.10 



99.76 



99.72 



DESMOSITES. 



Under the desmosites are included contact products composed of tlie 

 .same mineral constituents as the spilosites, but which show a distinctly 

 banded structure. As shown in the discussion of the spilosites, the two 

 must be very closely related and grade into each other. 



E. Kayser, from Roth'.s Cheni. Oeol., Vol, III, 1890, ji, 143, No. IV 



