354 



0. A. Derby — Association of Argillaceous 



Since the above was written I am enabled, through the ex- 

 treme kindness of Profs. Clarke and Hillebrand of the U. S. 

 Geol. Survey, to add the following very minute and painstak- 

 ing analysis of the peculiar rock from the Serra do Gigante, 

 which, as indicated in the above discussion, is the most prom- 

 ising for giving an idea of the hypothetical original rock 

 type from which the various schists here described may be 

 presumed to be derived. At my request special attention was 

 given to the detection of rare elements of which those of the 

 cerium group and lithia were, from a preliminary examination, 

 presumed to be present in an abundance that failed to be veri-' 

 tied. Contrary to expectation, the rock proves to be chloritic 

 rather than sericitic, though, as I am informed, the petro- 

 graphic examination made in Washington confirmed the opin- 

 ion formed here that the appearance of the predominant 

 micaceous element is that of a muscovite mica. Contrary to 

 expectation also, the rock proves to be basic rather than acid, 

 and thus the principal difficulty in the way of the attempted 

 affiliation with the Dattas and Sao Joao schists of diabasic, or 

 basaltic, aspect is removed. On the assumption, based on the 

 complete absence of recognizable allothigenetic elements, that 

 the original rock was eruptive, no affiliation with any known 

 type of which analyses are at hand can be made. 



Analysis \ 



of Cyanitic 



schist, from 



Serra do Gigante, near Dia- 





mantina, 



Brazil, by W. F. Hillebrand. 













Residue insol. 





Whole mass. 



HC1 extract. 



H 2 S0 4 ext. 



in H 2 S0 4 



Si0 2 



38-32 



10-78 



14-76 



(23*56) 



Ti0 2 



493 



•10 



•20 



(4-73) 



Zr0 2 



•09 



trace ? 



? 



(-09) ? 



A1 2 3 



28*16 



10-42 



14 : 77 



(13-39) 



Z e & 



2-24 



(1-78) 



(2-24) 



none 



FeO 



4-02 



(3-21) 



(4-02 



u 



(Ni, Co)0 



•04 



9 



(•04) 







MnO 



•16 



? 



(-16) 



_ 



CaO 



•32 



•34 



•32 





SrO 



trace 



? 



? 





MgO 



12-04 



9-34 



(12-04) 



none 



k 2 o 



1-11 



•26 



(-26) 



•85 



Na 2 



•16 



(•03) 



(-03) 



•13 



Li 2 strong trace 



strong trace 



(strong trace) 



faint trace 



H 2 0, 105 c 



•55 



(•55) 



(•55) 







H 2 0, 220° 



•45 ) 









H 2 0, 310° 



•22 V 



5-36 



6'80 



•66 



H 2 0, 310° 



+ 6-79 ) 









*.<>■ 



•47 



•47 



(•47) 







s 



trace 













F 



trace ? 















100-07 42-64 56-66 



No boron, nor rare earths. 



43-41 



