174 THE GEOLOGY OF MINNESOTA. 



[Amygdaloid. Diabase. Quartz, veinstones, 

 agates, caloite, nicsolites, etc. 



No. 101. AMYGDALOID. 



Overlying No. 100. 



Ref. Annual Report, ix, page 27; Annual Report, x, page 37. 



Mc/j. The cavities have been filled with laumontite and calcite. About one- 

 fourth to one-third of the bulk of the rock is occupied by these minerals. The inter- 

 vening rock matrix is also more or less porous, the cavities being generally empty. 



No section. 



Aye. Cabotian. N. H. w. 



No. 102. DIABASE. 



One of the alternating diabase sheets of the west bluff of Agate bay. Underlies No. 101. 

 Ref. Annual Report, ix, page 27; Annual Report, x, page 37. 



Meg. This rock, outwardly, contrasts with No. 101 in its color, being dark 

 greenish gray, while No. 101 is brown, the amygdaloidal spots being much lighter. It 

 is medium grained, and probably olivinitic, but neither amygdaloidal nor porphyritic. 



No section. 



Ayi>. Cabotian. N. H. w. 



No. 103. QUARTZ. VEINSTONES, AGATES, CALCITE, MESOLITE. ETC. 



From the layers at Agate bay. 

 Ref. Annual Report, ix, page 27. 



Meg. Quartz secretions are abundant in the form of agate, found as pebbles in 

 the beach at Agate bay, but these must be derived from the drift clay, of which there 

 is a heavy sheet, rather than from the rocks that immediately form the coast line. 

 The quartz found in the trap sheets, as above enumerated, is rather in the veins and 

 irregular openings in the rocks, and is not marked by those colored bandings to which 

 the term agate is applicable. It is very probable, however, that these same layers, 

 at points inland from the bay, carry quartz in the form of agate. This quart/, is 

 usually granular in appearance, except in the centre of geodes, where crystalline 

 facets present a glistening surface. It is frequently associated with calcite, which 

 forms independent masses distributed quite capriciously amongst the quartz, while 

 in the geodes the last-formed mineral is sometimes in the condition of fragile fibres 

 or spicules of laumontite, which also, in other places, was formed cotemporaneously 

 with quartz. 



In connection with some of the siliceous masses enclosed in this rock is a hard. 

 white, finely and radiatedly fibrous mineral which is intimately mingled with the 

 quartz. 



Mic. This finely fibrous mineral pierces the quartz individuals in all directions. 

 running through one and into the next with surprising freedom. The double refrac- 

 tion of the zeolite is very low, and it takes the colors of the quartz. In a rather 



