224 THE GEOLOGY OP MINNESOTA. 



[Aporhyolyte. 



No. 153. APORHYOLYTE. 



Baptism river. A contorted or brecciated, slaty, closely-jointed and laminated, reddish-brown rock, form- 

 ing the "gate" by which the river enters the lake, rising in bluffs suddenly at the lake shore and shutting in a 

 bayou in the river. This is also porphyritic, and has translucent, square crystals. 



Ref. Annual Report, ix, pages 38, 39; Bulletin ii, page 128. 



Meg. This is a brown, very fine-grained rock, laminated with narrow whitish 

 bands, the latter being nearly as abundant as the brown parts of the rock. The lam- 

 inae, while preserving a general parallel direction, are at times bent and twisted. 

 Sometimes the light-colored bands have a thin layer of quartz in the centre, in this 

 respect resembling No. 127. The hand specimen shows no phenocrysts. 



.Mir. The rock is composed of quartz in poikilitic areas holding the usual impu- 

 rities of these aporhyolytes and the feldspathic material. Much of this feldspar is 

 in larger grains than is usual in these rocks, and in places there are micropegmatitic 

 areas of quartz and feldspar. Some of the feldspars, which are probably orthocl<.t*<- 

 now much altered, have a tendency to exhibit crystal outlines. Scattered thickly 

 through the rock are small, often curving and branching, and more or less discon- 

 nected, rods of firiitfititc. 



One section. 



Aye. Cabotian. 



liemiirk. This again is probably the equivalent of the rock of the Great Pali- 

 sades, and like much of that it shows distinct flowage structure lamination. Some 

 of- the feldspar is regarded as original and not as a product of devitrification. In this 

 respect the rock resembles those described under No. 140, which contain distinct 

 feldspar crystals in the groundmass. u. s. o. 



No. 154. APORHYOLYTE. 



From Palisade No. 2, a short distance east of the mouth of Baptism river. 

 Ref. Annual Report, ix, page 39. 



Undistinguishable from the rock of the Great Palisades. This rock forms 

 a small sharp point, and a high wall facing south; dips northeast. 



Mic. Under the microscope it differs from the Great Palisades in presenting 

 large areas of poikilitic quartz, these embracing not only the microlitic matrix, but 

 the. phenocrysts of ijnaiiz, with the latter of which they generally agree in optical 

 orientation. There is an occasional phenocryst of f<-I(/xi><n; largely replaced by 

 ij/Kirtz and calcifc. 



Remark. This may not be from the same stratigraphic mass as the Great 

 Palisades. This is indicated by the order of stratification. Under the Palisades 

 is the great Beaver Bay diabase, while under this is a series of alternating trap and 

 amygdaloid layers. N. H. w. 



