17S THE GEOLOGY OF MINNESOTA. 



[Diabase. Thalite, calcite, 

 mesolite. Aporhyolite. 



No. 109. DIABASE (with olivine). 



From the falls of Gooseberry river, S. W. % sec. 22, T. 54-9. 

 Ref. Annual Report, is, page 28. 



This rock shows the same characters as No. 108, and is probably from the same 

 layer. There are in the slide evidences of the existence of a portion of the magma 

 still in a glassy state. Such areas are translucent and clear in ordinary light and dark 

 between the nicols, but yet showing an incipient crystallization, which in some cases 

 seems to allow light to pass as through included microlites. 



Age. Cabotian; probably the Beaver Bay diabase. N. H. w. 



No. 109A. THALITE, CALCITE, MESOLITE, ETC. 



From No. 109. Falls of Gooseberry river. 

 Ref. Annual Report, ix,-page 28. 



Numerous cavities in No. 109 are filled with secondary minerals. These 

 cavities are not always of the definite forms of amygdaloid, but are often large and 

 irregular. 



Mic. Among these secondary minerals are thalite, calcite and mesolite, the last 

 having the same appearance of positive and negative fibres as rock No. 103.* 



Age. Cabotian. N. H. w. 



No. 110. APORHYOLYTE. 



From sec. 12, T. 54-9, east of-Gooseberry river. Rises gradually from the level of the lake at the western 

 end, with an apparent "dip" toward the west; rises in a bluff about forty feet high, and recedes with a dip in 

 the other direction, after an extent of about forty rods. 



Compare Nos. 119, 127, 520, 519, with which this rock is closely allied. Compare, also, Nos. 68 and 74, of 

 which this rock seems to be the analogue if not the chronologic equivalent. No. 78, with which this rock was 

 compared in the field notes, is probably not the same kind of a rock. 



Ref. Annual Report, ix, pages 28-31, 38; Annual Report, x, page 38. 



Mic. This rock contains some porphyritic ifiitirtzes and some porphyritic crys- 

 tals of a plaiyoclase. The former are sub-rounded and were evidently generated 

 prior to the eruption which separated this rock from the parent magma. There is 

 also much quartz of later date, which embraces the small crystals of the other min- 

 erals poikilitically. 



The rock is wholly, but micro-crystalline, and approximates toward the " red 

 rock " of the region. The existence of a plagioclastic feldspar in a porphyritic con- 

 dition shows the magma was rather too basic to form a typical granite, but would 

 come nearer an andesitic rock. The most of the feldspathic crystalline matter is too 

 fine and too much stained with hematite to be susceptible of exact determination, 

 but it is presumed to be of orthoclastic composition. 



One section. 



Age. Cabotian. lied Rock series. N. H. w. 



*Voir 3fintralogie d? France, vol. ii, p. 278, where Lacroix says the allongeraent of mesolite is sometimes negative and 

 sometimes ]>ositive without intermixture of natrolite. 



