734 



J. A. UDDEN COMPOSITION OF CLASTIC SEDIMENTS 



hand, magnetite sand is better sorted than quartz sand because the former 

 has a comparatively high specific gravity. 



This principle is made nse of in the construction of ore separators, 

 and the laws governing its application are well known. To illustrate 

 its effect in natural sorting, fourteen analyses were made of seven sam- 

 ples of various sands, each consisting in part of quartz and in part of 

 magnetite. These analyses show that the chief constituents and the 

 admixtures when averaged for the two minerals are distributed relatively 

 as below: 



TaMe shotoing sorting in Water of clastic Elements of different specific Gravity 



Names of grades. 



Coarse admixtures. 



Maxi- 

 mum. 



Fine admixtures. 



4 



3 



2 



1 



1 



2 



3 



4 



Quartz sand 



Magnetite sand. . . . 



1,7 



2.7 

 .1 



8.5 

 6.9 



26,5 

 17.5 



41.1 



71.5 



15.8 

 3.7 



2.5 

 .1 



.1 













The quartz is distributed through eight grades and the magnetite 

 through only six. It is also found that the maximum of the quartz 

 grains in each pair of analyses was from one to three grades farther 

 toward the larger sizes than the maximum of the magnetite grains. The 

 distance between the two maxima in the seven pairs of analyses averages 

 near one and a half grades. (See Table 30.) 



List of Samples of Magnetite-l)earing Quartz Sand and Magnetite Sand in 



TaUe SO 



338. Magnetite-bearing quartz sand from Vie jo Canyon, Presidio County, 



Texas. 



339. Magnetite-bearing quartz sand from the beach of Lake Michigan, near 



Evanston, Illinois. 



340. Magnetite-bearing quartz sand from the bed of Tornillo Creek, Brewster 



County, Texas. 



341. Magnetite-bearing quartz sand from the beach of Matagorda Bay, Olivia, 



Texas. 



342. Magnetite-bearing quartz sand from the beach of Matagorda Bay, Olivia, 



Texas ; second sample. 



343. Magnetite-bearing quartz sand from the Limpia Canyon, Davis County, 



Texas. 



344. Magnetite-bearing quartz sand from a canyon in the Chinati Mountains, 



Presidio County, Texas. 



345. Magnetite sand in sample number 338. 



346. Magnetite sand in sample number 339. 



347. Magnetite sand in sample number 340. 



