NOVEMBEE 20, 1914] 



SCIENCE 



755 



such as tte ones described here, and can do so 

 without great difficulty with various school 

 abilities. 



Edward L. Thorndike 



Teachers College,. 

 Columbia University 



phosphate deposits in the mississippian rocks 

 of northern utah 



Since 1908 extensive work has been done 

 both by private individuals and the U. S. 

 Geological Survey to determine the amount 

 and character of the rock phosphate in the 

 Eocky Mountain region. The principal work 

 of the investigation of the deposits, however, 

 has been confined to the well-known horizon in 

 the rocks of upper Pennsylvania of Permian 

 age. It is now known that phosphate exists in 

 the Mississippian rocks in a zone more than 

 2,000 feet stratigraphically below the phosphate 

 horizon that has heretofore been given so 

 much study. 



The zone containing the phosphate is more 

 than 100 feet thick and consists of layers of 

 phosphate and black and brown shale with 

 interstratified layers of sandy limestone. In 

 extent it is known to outcrop in a north-south 

 direction for more than forty miles, and sec- 

 tions studied show it to have an area of more 

 than one hundred square miles. It has been 

 reported as far south as Ogden Canyon^ but 

 no detailed section has been measured in that 

 locality. 



On the east side of Cache Valley the phos- 

 phate rocks have been prospected for coal and 

 this exposure has given the best opportunity 

 for detailed study. The face of the mountains 

 which form the eastern boundary of the valley 

 is a weathered fault scarp which terminates 

 the western limb of a syncline. The ledges on 

 the face of the mountain are exceptionally well 

 exposed, the rock being principally bluish gray 

 limestones with thin beds of shale and quartz- 

 ite. Here the geologic section is well exposed 

 and shows Silurian rocks at the base and 

 Pennsylvanian at the top of the succession. 

 Only the lower members of the Pennsylvanian 

 or Permian are present in this locality. 



1 Blackwelder, TJ. S. Geol. Survey Bull., 430. 



Observations on the face of the mountains, 

 which extend more than 4,000 feet above the 

 valley, show that the rocks strike N. 10° to 

 14° E., and dip eastward from 20° to 30°. 

 The beds flatten to the eastward and about six 

 miles east of the face they rise again, the 

 strata on the eastern limb of the syncline dip- 

 ping as much as 10° to the west. Erosion has 

 clearly exposed the higher beds on the eastern 

 limb of the ssmcline.^ The phosphate rock is 

 exposed on both the east and west limbs of the 

 syncline which lies near the top of the range. 



The Logan Eiver has cut through the range 

 from east to west, and has made a good ex- 

 posure of all the strata included in the upper 

 part of the synclinal fold. The phosphate 

 zone, therefore, lies in two separate areas, one 

 to the north and one to the south of the river. 

 The Mississippian rocks are well up on the 

 western side of the mountains forming the 

 eastern boundary of Cache Valley and even in 

 the lowest part of the fold in the canyon they 

 are more than 1,000 feet above the river. 



The zone containing the phosphate is ex- 

 posed in a cliff of very compact bluish gray 

 limestone which is usually more than a hun- 

 dred feet thick and contains an abundance of 

 cup corals. At the base of this cliff there is 

 a lean phosphatic zone from five to seven feet 

 thick of shale containing a few bands of chert. 

 The shale also contains several thin layers of 

 oolitic rock phosphate ranging from one half 

 to one inch in thickness. One sample taken 

 from all of these layers yielded only 7.21 per 

 cent, tricalcium phosphate. This zone is prob- 

 ably of no economic value. It has been pros- 

 pected in a number of places for coal. 



The thicker and richer phosphate zone lies 

 just above the thick ledge of limestone. The 

 phosphate rocks are less resistant to erosion 

 than the underlying and ov3rlying limestone 

 ledges and the latter stand out more promi- 

 nently than the included softer beds. The 

 rocks in the phosphate zone which are gener- 

 ally dark colored contain thin bands of non- 

 phosphatic limestone with shale and some 



2 See Geological Map — parts of western "Wyom- 

 ing, southeastern Idaho and northeastern Utah — 

 Hayden survey, 1877. 



