357 



Soctioii North from ii<':ir ("Mmp Apiiclic (Fort ApMclic) (after Cilix-rt)).** 



Foct 



1. P,asiilt and iiasall ^'ravcl 70 



2. Palo pink slijilitly colu'rciit. massive sand and ixravcl resting,' 



unconformalily on No. .". -"rjO 



:;-(;. clastic rodvs KuO 



Total 2'2(;() 



It is quite possible from the data al hand that the dejiosits have 

 aeenmulatcd in Seven-mile Hill section and in the Salt Kiver and Hinton 

 i-esions and in many other places in the area, covered by this paper throuRh- 

 out the Tertiary and may have begun even earlier. A part of the series 

 which the writer had originally designated "Tertiary", principally in the 

 sections mentioned above, begins with a consolidated, coarse conglomerate 

 stratum, beneath which are strata of partly lithified sands, clays and 

 gravels reaching a thickness of nearly a thousand feet in thickness in some 

 places. The formation is found, for the most part, in the ancient canyons 

 of the region. Conformably on the formation above designated "Tertiary", 

 in this paper and in my original report on the region, ai'e hundreds of feet 

 of unconsolidated gravels and clays and occasionall.v volcanic ashes. This 

 series covered the entire region, excepting possibly the Ellison dome, so 

 that the lava flows which closed the Quaternary, flowed over a plain. Since 

 then much has been removed so that now it is patchy, except where it is 

 protected by superimposed lava. It now fills the valleys of the Pinal and 

 Apache mountain districts ; the volcanic and plutonic rocks projecting above 

 it as peaks and mountains. The middle Cherry creek valley and the Tonto 

 basin, as well as the Ellison flat, are covered with it. It covers the Mogolhm 

 mesa together with its southern prolongations, including the Cil)icu divide, 

 to a thickness of from five hundred to a thousand feet in many places. It 

 is the surface rock of much of the Kelley butte country, and extends beneath 

 the lava of the Nantan Plateau as far as visited. 



At the time the writer studied the region, he believed that these deposits 

 were due to a stage of ponding, as a result of differentral uplift and lava 

 flows, since he found no glacial striae; but since his study of the glaciation 

 in the San Juan mountains in Colorado and the Deep Creek region, Utah, 

 he has been compelled to change his views and conclude that the deposits in 

 iiuestion are of glacial origin and probably in part due to laking, as a 

 ri'sult of glaciation and volcanic disturbances. This view is also born out 

 by the fact that the Cibicu divide and the MogoUon mesa, which are both 

 heavily covered with this drift, are higher than the surrounding country 

 and show no evidence of a laking stage. 



Tlie deposits, clays, sands, gravels, and boulders of schist, quartzite, 

 gneiss, carboniferous rocks, vitreous Tonto .sandstone, diorite, trachyte, 

 rhyolite, and Archean rocks, indicate different development centers for the 



►Gilbert, ihid., p. 165. 



