384 ransome: the ray quadrangle 



brown. Most of the Mescal limestone is magnesian and a part 

 of the formation is dolomite, as may be seen at the Roosevelt 

 dam where the beds are well exposed in the spillway cuts. 



Between the limestone and the overlying Troy quartzite is a 

 layer of decomposed vesicular basalt whose maximum observed 

 thickness is from 75 to 100 feet. Although the basalt in places 

 is much thinner than this, the flow was apparently coextensive 

 with the Mescal limestone throughout the Ray and Globe quad- 

 rangles, and has been recognized as far north as Roosevelt. This 

 basalt, owing to its small thickness, has been mapped with the 

 Mescal limestone in the Ray quadrangle although it is not in- 

 cluded in the definition of that formation. The average 

 thickness of the Mescal limestone is about 225 feet in the Ray 

 quadrangle. 



The Mescal limestone has been recognized in the Sierra Ancha 

 and in the Santa Catalina Range. It is in part lithologically 

 identical with and is probably the stratigraphic equivalent of 

 the Abrigo limestone of Bisbee and Tombstone, which contains 

 Middle Cambrian fossils. This correlation, however, is not re- 

 garded as sufficiently well established to justify definite appli- 

 cation of the name Abrigo in the Ray area. 



In all of the regions where it has been identified the Mescal 

 limestone has been extensively invaded by intrusive sheets of 

 diabase and has suffered dismemberment as an effect of the 

 intrusion. In parts of the Ray quadrangle the formation is 

 represented only by detached masses of strata included in diabase. 



Troy quartzite. The name of this formation, which lies above 

 the Mescal limestone, is derived from Troy Mountain in the 

 Dripping Spring Range. Everywhere in the Ray quadrangle it 

 is separated from the limestone by the basalt flow and this may 

 possibly indicate some slight unconformity. No evidence of 

 erosion, however, has been detected either below or above the 

 basalt, which may have flowed under water. 



The beds of the Troy quartzite range from thin flaggy or shaly 

 layers to cross-bedded pebbly strata from 25 to 50 feet thick. 

 On the whole the thicker beds are characteristic of the lower 

 and middle portions of the formation. The upper part is invari- 



