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



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of the Nevada formation which is normally a gray fine grained, 

 ordinary sedimentary limestone is converted at the contact with 

 the monzonite into a snow white marble of much coarser texture. 

 At the contact of the monzonite with both shale and limestone 

 there are developed bodies of garnet rock which carries more 

 or less chalcopyrite and which can only be interpreted in a cer- 

 tain sense as a product of contact metamorphism. The mon- 

 zonite itself, moreover, has its character modified in the imme- 

 diate vicinity of the contact with the surrounding rocks. At a 

 shaft by the roadside immediately north of the Monarch claim, 

 for example, the monzonite at the contact is much finer grained 

 than at some little distance away, and presents the features of 

 a chilled edge of an intrusive mass. These facts, taken with 

 the others above enumerated, establish the intrusive hypothesis 

 upon a very satisfactory basis ; and in the absence of any evi- 

 dence of faulting leave it unquestioned. 



A small isolated area of the monzonite, occupying a few 

 acres upon the Sacramento, Schley and Good Enough claims 

 north of Pilot Knob, is regarded as an integral part of part of 

 the large mass underlying Weary Flat. It is separated from 

 the latter by but a few hundred feet. It cuts both the Nevada 

 limestone and the White Pine shale and has a well exposed con- 

 tact zone of garnet rock against the limestone. If erosion had 

 cut but a little deeper, the roof of sedimentary rocks in the 

 intervening space would have been removed and the two areas 

 thus shown to be one as indicated in the section C-D on the 

 accompanying geological map. 



Just beyond the confines of the map, however, on the Taylor 

 claim, north-northwest of Pilot Knob, there is another area of 

 the monzonite which may similarly be interpreted, or, inasmuch 

 as it cuts considerably higher into the sedimentary rocks, it may 

 be regarded as an apophysis from the same mass. The rock 

 here has more the facies of a quartz monzonite, there being a 

 little quartz present. It has associated with it garnet rock carry- 

 ing chalcopyrite as shown by prospecting operations. While it 

 is clear that the mass of monzonite of Weary Plat is an intrusive 

 batholith (or possibly laccolith), it seems also certain that the 

 intrusive process was pecidiar in certain ways. Usually in the 



