380 ransome: the ray quadrangle 



or no difference on their behavior as to losses on heating and 

 washing. 



The nature of the process of disintegration of platinum and 

 its alloys is briefly discussed in the complete paper, and sug- 

 gestions are there offered concerning the specifications of highest 

 grade platinum crucibles, including the substitution of rhodium 

 to 5 per cent for iridium, and the practical elimination of iron. 



GEOLOGY. — The Paleozoic section of the Ray quadrangle, Ari- 

 zona. F. L. Ransome, Geological Survey. 



Introduction. The geologic mapping of the Ray quadrangle, 

 for folio publication as part of the Geologic Atlas of the United 

 States, was completed in 1911. A year or more is likely to 

 elapse, however, before the folio can be published, and as in the 

 meantime there will be occasion in other publications to refer 

 to the Ray geologic section, it appears desirable that a brief 

 preliminary statement regarding this section and its nomen- 

 clature should be placed on record. 



Pre-Cambrian. The fundamental rocks of the region are the 

 Pinal schist, commonly a thinly laminated sericitic variety, and 

 granitic rocks intrusive into the schist. The Pinal schist con- 

 sists in the main of metamorphosed sedimentary rocks. Both 

 the schist and the granitic rocks are pre-Cambrian. Whether 

 they should be classed as Algonkian or Archean is a question as 

 yet undecided. 



Scanlan conglomerate. Resting as a rule directly on the worn 

 surface of the pre-Cambrian crystalline rocks is the Scanlan 

 conglomerate. The first description of this basal conglomerate 

 appeared in the Globe report^ where it was assigned a thickness 

 of from 1 to 6 feet and was characterized as being composed of 

 imperfectly rounded pebbles of white quartz, with occasional 

 flakes of schist, in a pink arkosic matrix. The name was de- 

 rived from Scanlan Pass in the northwestern part of the Globe 

 quadrangle. The conglomerate has since been found to present 

 considerable variation in character and thickness. In parts of 



> U. S. Geol. Survey, Prof. Paper No. 12, pp. 30-31. 1903. 



