184 THE GEOLOGY OF MINNESOTA. 



[Diabase. 



posed to be the same as the great gabbro range from Duluth to Pigeon point. The 

 other portion, which still is hardly separable from this, is more basic and allied to 

 the real traps of the region. It is, at any rate, very closely connected, structurally 

 and stratigraphically, with the " red-rock " series, and for the present that is all that 

 can be said of their origin. 



Aye. Cabotian (?); perhaps of the same origin and age as Nos. 632 and 635; 

 one of the thin lava sheets co temporary with crumbling conglomerates. 



Remarks. The stratigraphic order of the main rock masses, as made out along 

 this part of the coast, is given in Parts 1 and III. The exact nature of this rock 

 could not be made out in the field. It was sometimes believed to be a metamorphic 

 sedimentary rock, but.it was finally left unsettled until more detailed examination 

 could be made, with the following note: 



"As to the Two Harbor rock, its character and origin are still to be determined 

 by more minute examination of the samples collected, and by further field observa- 

 tions. It has been referred to as a metamorphic rock, in some of these notes, but 

 it has also very much the aspect of a fine-grained igneous rock. It has the jointage 

 as well as the general homogeneity of trap; the red bands crossing it and the geodic 

 spots seen on its surface, perhaps having originated from the overlying sedimentary 

 conglomerate. It does not have the appearance of being exactly the equivalent of 

 the quartzless red rock at Duluth, but it must occupy very nearly the same strati- 

 graphic position." (Tenth Annual Report, page 115.) 



From a careful correlation of notes made on the stratigraphic order of the erup- 

 tives of this locality, published in the ninth and tenth annual reports, and a com- 

 parison of petrographic characters, this rock is placed below a series of alternating 

 trap and amygdaloid sheets represented by the Gooseberry River series and probably 

 by the Agate Bay series. (Compare No. 176.) There may be, however, a fault by 

 which the Two Harbor rock has been lowered, its horizon being about the same as 

 Nos. 632 and 635, i. e., Manitou. N. 11. w. 



No. 118. DIABASE (with olivine). 



Conical hill at the head of Two Harbor bay. 

 Ref. Annual Report, ix, page 31. 



Meg. There are two hand specimens of this rock. The first is a medium grained 

 diabase, presenting a somewhat earthy, decayed appearance, and there has been a 

 slight reddening of the rock. The second is a fresh, lustre-mottled diabase, and was 

 evidently picked up on the lake shore. The weathered surface shows indistinctly 

 large gray areas between which are narrow bands of a darker greenish yellow color. 

 There are a few small areas which appear like diabase of coarser grain than the 

 mass of the rock. 



