PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 277 



Diabase. Caloite. Basalt. Gabbro.] 



No. 246. DIABASE (with olivinej. 



About three-fourths of a mile east of Deronda bay, at the mouth of a little creek; near the centre of sec. 

 19, T. 63-6 E. 



Ref. Annual Report, ix, page 60. 



Meg. A dark-gray to greenish, fine-grained diabasic rock appearing much 

 decayed. It contains much calcite, some of which is pinkish. 



Mir. A diabase with the abundance of feldspar and the large plates of mtyite 

 seen in No. 245. There are, however, more of the altered olivines than in No. 245, 

 and what is peculiar is that the interior of these altered grains is frequently a clear, 

 subangular grain of quartz surrounded by the usual decomposition products of the 

 olivine. 



One section. [ It is possible that the section marked No. 246 is not from the 

 hand sample of that number. The latter appears more decayed than is indicated by 

 the section.] 



Age. Manitou(?) u. s. G. 



No. 246A. CALCITE. 



From No. 246. 



Ref. Annual Report, ix, page 60. 



Meg. A mass of calcite in small, transparent crystals and also massive and 

 flesh colored. 

 No section. 



Age. Manitou(?) u. s. G. 



No. 247. BASALT. ( Amygdaloidal. ) 



Rock similar to No. 246, but more amygdaloidal. 

 Ref. Annual Report, ix, page GO. 



Meg. A fine-grained, much decayed, dark -greenish gray, diabasic rock. It con- 

 tains am ygdules of calcite, both pink and colorless; also of chlorite and chalcedony. 

 Much chlorite permeates the rock. 



Mic. The section, which is too thick, shows plagiocldse mici'oliths in a dirty, 

 confused mass of alteration products chlorite, calcite, iron ores and a little quartz. 

 It is impossible to tell what the original nature of this groundmass was, but it seems 

 probable that part of it, at least, was glassy. 



One section. 



Age. Manitou(?) u. s. G. 



No. 248. GABBRO. (Altered. ) 



From a dike which has an indefinite width, at least 200 feet, on the third little point east of Deronda bay, 

 after a pebbly beach of half a mile. The second point is like rock No. 246. 

 Compare rock No. 41, at Duluth, and No. 1855. 

 Ref. Annual Report, ix, page 60. 



