PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 783 



Quartz. Agglomerate.] 



pyrite, and the rest of the nodule is made of pyrite radiating out from this mass. In 

 another nodule the centre is about an inch in diameter, and the radiating border 

 only a quarter of an inch in thickness. No section. 



Age. Archean (Keewatin). u. s. G. 



No. 1509. QUARTZ. ( c/Ki/rcilanir n.-his.) 



In the jaspilyte on the top of Chester peak, near Soudan. 

 Ref. Annual Report, xviii, pages 11, 59. 



Meg. Small, white veins, apparently of the same constitution as white jaspilyte, 

 cross red jaspilyte. No section. 



Age. Archean (Keewatin). u. s. G. 



No. 1510. AGGLOMERATE, (liasic.) 



Ely. Prom the agglomerate at the railroad cut. 



Ref. Annual Report, xviii, pages 13, 59 ; American Geologist, vol. ix, pages 359-368. Compare Nos. 1624 

 and l(i-J5. 



Meg. Collected so as to show the forms of two boulders and the darker green 

 rock separating them. 



Mir. One section is from the interior of one of the boulder forms, and the other 

 from the edge of the rounded mass. That from the interior shows a fine diabasic 

 structure in the arrangement of the minute chlontic feldspars, which are radially 

 arranged, for the most part, but are in other places grouped in a somewhat parallel 

 arrangement. They are much altered, but reveal a fine albite twinning without 

 distinct terminations. The surrounding material is dimmed by much alteration, 

 but occasionally a grain of /n/ro.raic is seen in the mass. Tt also contains calrifr. 

 /(iiro.i-1'itc, and apparently a few Jiornlih'tnles and some traces of a secondary feldspar. 



The other section is completely altered. It shows no diabasic structure. The 

 distribution of leucoxene is the most marked regular feature. At one side of the slide 

 it is in annular groups and roundish nests of about uniform size. By degrees, depart- 

 ing from this part of the slide, these become larger, but thinner, and so dispersed at 

 last that on breaking up they spread more and more diffusely, coalesce and cause a 

 general dissemination of leucoxene throughout the slide. The most concentrated 

 portion of this leucoxene is associated with a micro-granulitic generation of 

 secondary (?) feldspars. These little grains do not interlock; indeed, they are entirely 

 isolated and free from each other and may represent a feldspathic sand. In the midst 

 of them are also a few pi/ro.m/<'( ? ) grains. Suddenly appears, in the midst of this 

 structure, a rectangular network of bright spicules whose individual cross-sections 

 with the highest power have about the thickness (apparent) of the spider lines, and 

 also have parallel extinction. They are too fine to be determined, but appear to be of 

 m-tinolite. The rest of the slide appears to consist of a uniform granular mixture of all 



