Vol. 4] Lawson. — The Robinson Mining District. 



297 



tunity for systematic search. Some of the beds of this forma- 

 tion are almost black limestone. The thickness of the formation 

 is unknown as only the upper part of it comes within the limits 

 of the country examined. It was estimated, however, that its 

 thickness was not less than 1,000 feet and might be much more. 



CORRELATION WITH THE EUREKA SECTION. 



For the purpose of comparing the geological column of the 

 district under consideration with that of the Eureka section, the 

 following correlation of all the Palaeozoic formations is sug- 

 gested : 



Eobinson Mining Dist. Eureka. 



/ Feet Feet 



| M \Euth limestone .... 500+ Upper Coal Meas 500 



g o 'Arcturus shaly limestone. 1,000 Weber Conglomerate 2,000 



)Ely limestone 1,500 Lower Coal Meas 3,800 



° ( Diamond Peak Quartzite. . 3,000 



i [White Pine shale 1,000 White Pine shale 2,000 



% 2 ] Nevada limestone 1,000+ Nevada limestone 6,000 



GENERAL STRUCTURE. 



In the study of the general geological structural relations 

 of the Robinson Mining District several factors have to be con- 

 sidered. These are: (1) The stratigraphic sequence of the De- 

 vonian and Carboniferous formations as above outlined. (2) 

 The flexure of these strata. (3) The relation of the folded strata 

 to the irruptive masses which cut them. (4) The features intro- 

 duced in the process of mineralization. (5) The lavas and tuffs. 

 (6) The faulting of the region. Having in the previous section 

 described the stratigraphic sequence, we may now conveniently 

 consider that phase of the structure referable to the deformation 

 of the Palaeozoic rocks anterior to the appearance of the irrup- 

 tive rocks leaving the discussion of the other factors till later. 



The dominant feature in the structure of the Palaeozoic rocks 

 is a broad syncline, the axis of which runs nearly north and 

 south, through the Ruth Mine, and pitches northerly at a con- 

 siderable angle. In the central part of this fold lies the Ruth 

 limestone with synclinal dips at moderately low angles. Plank- 

 ing the Ruth limestone on either side is the Arcturus shaly 

 limestone dipping under it. Flanking this on both sides is the 



