Mansfield — Western Phosphates of United States. 595 



source; or (c) the lands adjacent to the waters of 

 deposition were so low, through base leveling or other- 

 wise, that they furnished little clastic material to the 

 sea; or (d) following an earlier suggestion of Hayes. 13 

 strong marine currents may have swept away the fine 

 terrigenous material, leaving only the phosphatic oolites. 

 The physiographic conditions changed from time to time 

 during the deposition of the phosphatic shales, for beds 

 of shale, sandstone, and limestone, some of which are 

 more or less phosphatic, are interbedded with the more 

 nearly pure phosphate. 



(3) The period of deposition may have been long. The 

 time required for the deposition of the phosphate beds 

 and the accompanying Permian strata is not known but 

 some data permit suggestive comparisons. It has been 

 stated that there is at least local unconformity at the base 

 of the Phosphoria formation. This is not, however, 

 regarded as indicating any great time interval. The top 

 of the formation may also mark a disconf ormity and the 

 f aunal change above is very pronounced. The time inter- 

 val here may be large but on the other hand the faunal 

 change may have been produced by the geographic 

 changes of the late Permian or early Mesozoic without 

 greater lapse of time here than, elsewhere. The phos- 

 phatic shales, with which are grouped some non-phos- 

 phatic or lean shales, sandstones and limestones, are 

 about 150 feet thick, and of this thickness the actual beds 

 of phosphate rock form only a small proportion. The 

 Phosphoria formation as a whole, representing all the 

 known Permian of the region, is about 500 feet thick. 

 The Permian section in Kansas, according to Prosser, 14 

 is about 2,000 feet thick; in Texas the Permian forma- 

 tions are reported as 5,000 feet thick 15 and in Oklahoma 

 as 2,600 feet thick. 16 If these various deposits may be 

 regarded as occupying time intervals at all similar, it is 

 obvious that the deposition of the Phosphoria formation 

 of Idaho was at a much slower rate than the accumulation 



13 Hayes, C. W., Tennessee phosphates, U. S. Geol. Survey, Seventeenth 

 Ann. Kept., pt. 2, p. 534, 1896. 



14 Prosser, C. S., Revised classification of the upper Paleozoic formations 

 of Kansas, Jour. Geology, vol. 10, pp. 703-737, 1902. 



15 Cummins, W. F., Eeport on the geology of northwestern Texas, Geol. 

 Survey Texas, Second Ann. Kept,, pp. 359-5*52 (p. 398), 1891. 



16 Beede, J. W., Invertebrate paleontology of the upper Permian red beds 

 of Oklahoma and the Panhandle of Texas, Kansas Univ. Sci. Bull., vol. 

 4, Xo. 3, pp. 113-171 (p. 136), 1907. 



