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



293 



thinner layers of limestone which on weathered surfaces are 

 etched out. The layers or laminae are distinctly curved. In 

 thin section the alternating laminae are distinct (the limestone 

 being' tnrbid from impurities and the chert clear. The line be- 

 tween the chert and limestone is sharp but is irregular. The 

 chert is a crypto-crystalline aggregate of quartz grains showing 

 aggregate polarization effects. There are some shred-like areas 

 of calcite in the chert layers. The limestone is an allotriomorphic 

 granular aggregate of calcite grains of rather vague boundaries. 

 There is an abundance of fragments of organisms both in the 

 limestone and in the chert layers. These organisms appear to be 

 chiefly foraminifera. In the chert the cavities of the organisms 

 are filled with an aggregate of quartz grains of much larger 

 size than those composing the chert matrix, but the chamber 

 walls are still composed of calcite. The same statements are true 

 of the organic remains in the limestone, but silicification of the 

 cavities is less pronounced. In several cases chambered shells 

 were found partly in the limestone and partly in the chert but 

 the character of the shells appeared to be the same for both parts. 



Fossils. — The time at the disposal of the writer while in the 

 Robinson district did not permit of a deliberate search for pa- 

 la eontological evidence of the age of the formations, but wher- 

 ever fossils were observed in the course of the stratigraphic 

 work they were . collected. The localities at which such fossils 

 were found are chiefly confined to the Ruth limestone. These 

 were submitted to Mr. George H. Girty, the well known specialist 

 on the Carboniferous who kindly identified the following forms : 



Fusulina cylindrica. 

 Zaplirentis sp. 

 Stenopora sp. 



Productus aff. P. porrectus Kut. 

 Fusidina elongata (?) 

 Seminula subtilita. 

 Lithostrotion, mammillare (?) 

 Diphyphylhim n. sp. 

 Lonsdaleia n. sp. 

 Lonsdaleia n. sp. var. 



Of this fauna Mr. Girty states that it belongs in the Upper 

 Carboniferous and rather well up. While some of the forms 

 possess more satisfactory evidence than others, he feels little 



