PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 561 



Dolomyte. Diabase.] 



No. 824. DOLOMYTE. 



Taylor's Falls. The upper portion of the matrix embracing the conglomerate where excavated for the 

 railroad at the highway crossing, southern part of the village. 

 Ref. Annual Report, x, page 117.' 



Meg. Completely crystalline, each grain of which is a perfect crystal of rhom- 

 bohedral habit, containing fossils of Lingulae and nodules of coarse calcite crystals. 

 Passes upward into regular beds of dolomitic limestone. 



Mic. The only substances visible belonging to the rock are the rhombohedral 

 crystals mentioned, of dolomite and a few small, scattering, angular grains of quartz. 



Age. Upper Cambrian. N. H. w. 



No. 825. DIABASE. 



Boulder from the conglomerate. (See Nos. 823 and 824.) 



Ref. Annual Report, x, pages 117, 118. Cf., also, C. P. BKRKEY: "The Geology of the St. Croix Dalles," 

 American Geologist, vol. xx, pages 345-383; vol. xxi, pages 139-155, 270-294. N. H. WINCHELL: "The Signifi- 

 cance of the Fragmental Eruptive Debris at Taylor's Falls, Minnesota," American Geologist, vbl. xxii, pages 72-78. 



Meg. A considerably altered, rather soft, dark brownish diabasic rock. On 

 one side of the specimen is a coating of impure malachite. 



Mic. The section shows a highly altered diabase. The outlines of the lath- 

 shaped feldspars can be distinguished in places, but this mineral is highly altered, 

 clouded and kaolinized. Aside from the altered feldspars are iron ore (magnetite and 

 limonite), chlorite, epidote and some quartz. The whole section is in fact a confused 

 mass of secondary products. 



One section. 



Age. Boulder in Upper Cambrian. u. s. G. 



No. 826. DIABASE. 



At the top of the hill north from No. 825. 



Ref. Annual Report, x, page 118; Bulletin ii, page 119. 







Meg. A dark-green, fine-grained, diabasic rock, with considerable epidote. 



Mic. M. E. Wadsworth's description of this section is as follows:* 



" The section is that of a highly altered diabase, the only portions of its original 

 structure being the remains of the divergent feldspars and some apparent opacite 

 pseudomorphs after olivine. The rock now is composed of granules and plates of 

 secondary minerals like green fion/l/lende, chlorite, viridite, epidote, quartz, feldspar, 

 ferrite, opacite, magnetite, etc. The epidote, in pale yellowish granules, is abundant." 



One section. 

 Age. Cabotian. u. s. G. 



*Bullctin ii, p. 119. 



