PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 223 



Diabase. Aporhyolyte.] 



No. 150. DIABASE. 



Baptism river. Basaltic rock nearly in contact with No. 149, but so separated from it by debris of pebbles 

 etc., that its stratigraphical relations to it cannot be seen. 

 Ref. Annual Report, ix, page 38. 



Meg. A medium-grained, lustre-mottled diabase. Probably part of the great 

 Beaver Bay sheet mentioned before (see, especially, remarks under No. 148). 

 No section. 

 Age. Cabotian; Beaver Bay diabase. u. s. G. 



No. 151. APORHYOLYTE. 



Baptism river. A short distance below No. 150. Occupies the bed of the river at first, but gradually rises 

 so as to form high bluffs. 



Ref. Annual Report, ix, pages 38, 39. 



Meg. A very fine-grained, pinkish-gray rock with phenocrysts of quartz and a 

 gray to flesh-colored feldspar, some of which, at least, is plagioclase. 



Mic. A good example of an aporhyolyte with poikilitic quartz in the ground- 

 mass. In this case, however, the feldspathic material of the groundmass is in larger 

 grains than are common in the similar rocks already described. The feldspar pheno- 

 crysts are altered and clouded, but some still show two sets of twinning lamellae cross- 

 ing each other almost at right angles, and thus resembling microcline. A cleavage 

 section parallel to the base of one of the fresher feldspar crystals gave an extinction 

 angle of about 2.7. This section shows very minute twinning lamellae which, unless 

 carefully examined under a high power, are easily mistaken for cleavage lines. T.he 

 section also appears perpendicular to the optic plane. The latter fact, as well as the 

 very minute twinning lamellae, would indicate that the feldspar was anorthoclase, 

 rather than oligoclase. A micro-chemical preparation, with hydrofluosilicic acid, 

 showed large amounts of soda and a little potash. 



Age. Cabotian; red-rock series. 



JtaiHir/,-. Evidently this rock is the equivalent of the Great Palisade rock (Nos. 

 188 to 140) and of No. 145. Just below it, on the right bank, is an outcrop of rock 

 like the aporhyolyte of Beaver bay (No. 127). u. s. G. 



No. 152. DIABASE. 



Baptism river. Finely jointed, compact, basaltic, forming a precipitous high shore on either side of the 

 river, letting the river down to the lake level. This is dike-like in character of rock, but confused and brecciated 

 in outward aspect, forming irregular knobs and escarpments. This is found after an interval of non-exposure 

 in the river bed, after (below) the last. 



Ref. Annual Report, ix, page 38. 



Meg. A very fine-grained, almost aphanitic, compact, heavy, dark-brown rock, 

 looking like a fine diabase. 

 No section. 

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



