572 THE GEOLOGY OP MINNESOTA. 



[Calcite and laumontite. Diabase. 



Mic. The section is composed essentially of feldspar. This is much clouded 

 and to some extent reddened by dust-like hematite inclusions. Some of it appears to 

 be orthodase and some is plagioclase. The plagioclase shows equal extinction angles 

 up to about 13; it is optically negative, and sections cut almost perpendicular to 

 the obtuse bisectrix give extinction angles of 73 and 77. The feldspar is thus a 



r 



basic oliyoclase. Pyrite, calcite and green chloritic material are present in small 

 amounts. One section. 



Age. Cabotian. u. s. G. 



No. 853A. CALCITE AND LAUMONTITE. 



Prom a vein at Mannheim's silver mine, Duluth. 

 Ref. Annual Report, xiii, page 40. 



Mey. Calcite and pink laumontite. The latter is in needle-like forms in a finer 

 matrix of apparently the same mineral. 



Mic. The slide is composed essentially of laumontite. Some calcite and green 

 chloritic material are also present. 



One section. 



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



No. 853B. CALCITE. 



Prom a vein at Mannheim's silver mine, Duluth. 

 Ref. Annual Report, xiii, page 40. 



Meg. Rhombs of white calcite. 



No section. 



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



No. 854. DIABASE. 



Taylor's Falls. Compare Nos. 797, 820-822. 



Ref. Annual Report, xiii, page 40; Bulletin ii, page 114. 



Meg. A fine-grained, greenish diabase showing " lustre-mottling." 



Mic. M. E. Wadsworth's description of this slide is as follows:* " The thin 

 section is similar to No. 797, but it has suffered further alterations. In the section 

 are light green spots surrounded by a darker, greenish-brown groundmass. The 

 light green spots are formed by augite individuals dissected and generally with the 

 component parts entirely separated by the altered plagioclase and viridite. Some- 

 times these augite masses show in polarized light that they are composed of two or 

 more individuals. The groundmass is mainly composed of chlorite, viridite, epidotv, 

 feldspar, ferrite, opacite, and some pseudomorphs, apparently after olivine." 



One section. 



Age. Cabotian. 



*Sulletin ii, p. 114. 



