PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 573 



Graywaeke. Laumontite.] 



Sandstonu and shale. 



Remark. This rock was stated when collected to contain metallic copper in 

 minute particles. The small hand specimen at hand does not show these particles 

 of copper, as oxidation since the specimen was collected has quite likely obscured 

 them, and they do not seem to be present in the slide. u. s. G. 



No. 855. GRAYWACKE. 



" Dark concretions from the slates at Thomson, thought by Hunt and Dawson to contain a keratose sponge." 

 Ref. Annual Report, xiii, page 40. 



Mey. A fine-grained graywacke in which is part of a coarser-grained, softer, 

 rusty-weathering mass. 



Mic. The section was evidently made from the graywacke and shows small, 

 more or less angular grains of quartz and feldspar in a greenish cement. Under a 

 high power this cement is seen to be composed essentially of chlorite, quartz and 

 minute Muscovite scales. 



One section. 



Age. Animikie. 



Remark. Compare Nos. 1607, 1609 and 1611. u. s. G. 



NO. 856. X/AUMONTITE. 



Vein in Gabbro at Rice's point, Duluth. 

 Ref. Annual Report, xiii, page 40. 



Meg. The vein is composed mainly of fine-grained red laumontite. There is a 

 little greenish soft material also present. Piercing the fine-grained laumontite are 

 small colorless needles, and similar needles exist in radiating bunches on the side of 

 the vein. 



Mic. The section shows the colorless needles, which appear to be laumontite 

 embedded in a fine-grain red mass, apparently consisting of small grains of the same 

 mineral. 



One section. 



Aeg. Vein in Cabotian rocks. u. s. G. 



No. 857. SANDSTONE AND SHALE. 



Fond du Lac. 



Ref. Annual Report, xiii, page 40. 



Meg. The specimen consists of soft red shale and gray sandstone intimately 

 intermingled in a breccia or conglomerate, the sandstone acting as the matrix. The 

 shale occurs as fragments, large and small, and as interrupted bands in the sandstone. 

 In the sandstone are also a few pieces of a greenish-gray shale and in the red shale 

 are spots of a color similar to the greenish-gray shale in the sandstone. 



Mic. The section is made from the sandstone, but includes small pieces of the 

 shale, which is dense and red. The section is too thick for careful study, but it 



