386 ransome: the ray quadrangle" 



If the Mescal limestone is the same as the Abrigo limestone, the 

 Troy quartzite of course may represent Ordovician or Silurian 

 time, but in the absence of fossils or distinct unconformities it 

 appears safer to consider this quartzite as provisionally of Cam- 

 brian age. The entire group has been considered Algonkian,^ 

 partly because of a supposed resemblance to the Algonkian 

 rocks of the Grand Canyon and partly because the quartzites 

 at Roosevelt were erroneously thought to be unconformably 

 overlain by the Carboniferous limestone. A. B. Reagan"^ also 

 appears to have included a part of the group in the Algonkian 

 while calling what is here designated the Troy quartzite, Tonto 

 (Cambrian) . 



It is possible of course that a part of the group may be pre- 

 Cambrian, but the apparent conformability of the whole group 

 with the overlying Devonian, taken in connection with the great 

 unconformity between the basal Cambrian of the Grand Canyon 

 with the Algonkian (Unkar and Chuar), lends little support to 

 this view. Additional improbability is cast upon it by the dis- 

 covery in 1914 that a series of quartzites and shales in the 

 northern part of the Mazatzal Range, hitherto undescribed, are 

 unconformably overlain by some of the formations of the Apache 

 group. The results of this reconnaissance will be brought out 

 more fully in another paper. The hard quartzitic pebbles in 

 the Barnes conglomerate evidently came from the erosion of 

 these older quartzites of the Mazatzal Range. As at present 

 defined therefore the Apache group embraces the apparently 

 conformable series of supposedly Cambrian sedimentary rocks 

 of central Arizona. Should some of the beds turn out to be 

 other than Cambrian the group name will have to be corre- 

 spondingly restricted or may perhaps be abandoned as no longer 

 a convenient designation for a major stratigraphic unit. 



Martin lirnestone. Conformably overlying the Troy quartzite 

 is a series of limestone beds, some of which carry abundant and 



* Lee, W. T., Underground waters of Salt River Valley, Arizona. U. S. Geol. 

 Survey, Water-Supply Paper No. 130, p. 96, and fig. 11 on page C7. 1905. 



* Geology of the Fort Apache region, Arizona. Amer. Geologist 32: 277. 

 190.3. 



