100 PROCEEDINGS OF THE PHILADELPHIA MEETING 



After the injection of the quartz porphyry the magnetite-apatite ores separated 

 out of its magma in small, nodular units. Many of these units settled to the 

 bottom of the quartz iwrphyry magma, forming the main ore bodies at the con- 

 tact with the somewhat older, underlying syenite porphyry. Many other units, 

 now angular as well as round, were frozen in at higher levels; these are the ore 

 inclusions of the Aisible quartz porphyry — bodies which some authors have 

 hitherto regarded as xenoliths, thereby obscuring the genetic problem. 



Presented l)y title in the absence of the anthor. 



ORIGIN OF THE ROCKY MOUNTAIN PHOSPHATE DEPOSITS 

 BY ELIOT BLACKWELDER 



(Ah sir act) 



The author presents this as a preliminary statement concerning the origin 

 of the Rocky Mountain phosphate deposits. 



Among the world's known deposits of lime-phosphates at least six genetic 

 varieties have been clearly recognized: 



Primary : 



Pegraatitic (for example. Norway). Gumio (for example, Redonda Is- 

 land), Marine sediments (for example, Tunis). 

 Secondary or Metamorphic : 



Surface residual concentrations (for example. Quercy). Phosphatized 

 limestone and other rocks (for example, Florida "hard phosphate"), 

 Detrital deposits (for example, Florida "river pebble"). 



The voluminous Permian (?) phosphate strata of Wyoming, Idaho, and ad- 

 jacent States are marine sediments analogous to dolomite and limestone. 

 Some points about their origin have already been establishec . Girty. Gale, 

 or other observers. These are considered, and to them are added other safe 

 inferences as to the conditions of origin. The Rocky Mountain phosphatic 

 beds apparently resemble those of Algeria-Tunis, Belgium, Wales, Sweden, and 

 Tennessee (Devonian only) ; but are unlike tho.se of Estremadura (Spain), 

 southern France. Norway, Florida, the Carolinas, and the Peruvian Islands. 

 They belong, therefore, to the third class above noted. The foreign deposits 

 most resembling those of the Rocky Mountains have been carefully studied, 

 and the best interpretations of them, appropriately modified, seem to apply 

 quite as well to oui- western beds. Dmltting arguments, the chief points in the 

 partial explanation thus far elaborated are the following : In the ocean special 

 conditions of currents, temperature, etcetera, not yet understood, may have 

 induced the wholesale killing of animals over a large area and accumulation 

 of the putrefying matter on the sea-floor in moderate and shallow depths. 

 Anerobic decomposition produced ammoniacal solutions which dissolved the 

 solid calcium pho.sphate present in bones, teeth, brachiopod shells, and tissues. 

 The putrefactive conditions also prevented the existence of sessile bottom 

 organisms, and most calcareous shells descending from the surface were prob- 

 ably dis.'^olved i\v the abundant carbonic acid arising from the decay. For 

 physico-chemical reasons, already partly understood, the pho.sphatic materials 



