CONSANGUINITY OF ERUPTIVE ROCKS. 605 



was not observed in time to be included in the material sent to 

 Dr. G. H. Williams for study. Apparently there is a group of 

 gabbro and diabase-like rocks whose genetic relations are with 

 the nepheline-bearing rocks rather than with the ordinary mem- 

 bers of the groups which they so closely resemble. 



The peculiar and varied group of basic dyke rocks recently 

 denominated monchiquites by Prof. Rosenbusch, afford evidences 

 of consanguinity by their almost constant association, as apophy- 

 ses, with the nepheline-bearing eruptive centers to whose imme- 

 diate vicinity they appear to be limited. If certain decomposed 

 dykes at Caldas and Ipanema are correctly referred, this group 

 occurs at all the Brazilian localities. A single instance of a basic 

 segregration resembling this type has been observed in a dyke 

 of phonolite. The occurrence within the space of a few meters 

 in the Tingua phonolitic tuffs of three small dykes of this type, 

 of which two, standing alone, would be taken as representing 

 tephrite and limburgite is suggestive of another line of consan- 

 guinity. Equally suggestive is the occurrence of vosgesite in the 

 vicinity of the Jacupiranga center of eruption. 



Finally the evidence of volcanic action in the presence of 



fragmental eruptives found at all of the five localities in constant 



association with types ordinarily regarded as plutonic, such as 



augite-syenite, is exceedingly suggestive. 



Orville A. Derby. 

 Sao Paulo, Brazil, Aug. 1, 1893. 



