394 THE GEOLOGY OF MINNESOTA. 



(Diabase. 



No. 515. DIABASE (or fine-grained gabbro). 



At Sucker river; crosses the mouth of the river; runs northeast. Compare No. 89. 

 Ref. Annual Report, is, page 24; Annual Report, x, page 36. 



Meg. Brownish green, fine grained. 



Mic. The great multitude of little augites antedated the microlitic feldspars, 

 but occasionally a large augite is seen to be cut ophitically by the feldspars and also 

 to include augite grains having different orientation, apparently of the older genera- 

 tion. Magnetite now largely replaces the olivines. There is a confusion of 

 indeterminable secondary products, such as chloritic substance, bowlingite (?), 

 biotite(?), hematite (?) 



One section. 



Aye. Cabotian. 



Hriintrk. The date of the augites, with respect to the feldspars, in this fine- 

 grained rock, is like that in some of the coarse-grained gabbros. N. H. w. 



No. 516. DIABASE. 



Forms the bed of the stream at the mouth of Sucker river, and appears like a bed of lava. This disinte- 

 grates into globules and rots to a great depth before falling away. 

 Ref. Annual Report, ix, page 24; Annual Report, x, page 30. 



Meg. Heavy, dark green and almost black when wet. 

 Mic. The section shows an ordinary diabase with ophitic structure. 

 One (poor) section. 



Age. Cabotian. N. H. w. 



No. 517. DIABASE. ( GaUbroid. ) 



From the foot of the bluff, on the north side, at the mouth of Gooseberry river. Compare No. 108. 

 Ref. Annual Report, ix, page 28; Annual Report, x, pages 37, 38. 



Meg. A fine-grained diabase, with some red mottling. 



Mic. The section shows that in general the augite preceded the feldspars. The 

 crystals of augite are small, but are independent of the feldspars, yet occasionally 

 there is a larger augite which was of later date, as it is cut by the feldspars in an 

 ophitic manner. Whether there is any chemical difference between the augites of 

 different dates would be an interesting point to determine, but optically they appear 

 much alike. The crystalline form in neither is perfect. 



One section. 



Age. Cabotian. N. H. w. 



No. 518. DIABASE. 



From the top of the low bluff at the south end of the beach at the mouth of Gooseberry river, containing 

 amygdules of chalcedony. Furnishes some of the pebbles and all of the agates of Gooseberry beach. This rock 

 slopes into the water, and, where it is constantly under the action of the waves, it is reddish, like the pebbles. 

 but the pebbles mostly come from another bluff farther east, and are more acid. Compare No. 108. 



Ref. Annual Report, ix, page 28; Annual Report, x, pages 37, 38. 



