146 THE VERMILION IRON-BEARING DISTRICT. 



the peripheral and concentric arrangement of the amygxiules in the eUipsoids 

 were confirmed by repeated observations on similar occnrrences in the 

 Vermilion district. At one place on the hill just west of Ely and not very 

 far from the last house in the town, it was noticed that the amygdules were 

 concentric on one side of the ellipsoids, although a few were scattered 

 through the ellipsoids. In this case the exposure showed a transition from 

 amygdaloidal ellipsoidal rock to amygdaloidal nonellipsoidal basalt, both of 

 essentially the same grain. The exposure is about 20 paces in width north 

 and south. It looks very much as though the ellipsoidal portion of this 

 ancient lava represents the surface of the flow, which was more viscous 

 than the inner portion and consequently more readily broken. This 

 being true, such a relationship readily explains the occiu-rence of a transi- 

 tion from ellipsoidal to nonellipsoidal forms of the same rock, as discussed 

 in detail in Monograph XXXVI, to which reference has repeatedly been 

 made. Such gradations in these ancient lavas are shown by a number of 

 observations taken at different places. One passes in the field from a fine- 

 grained amygdaloidal ellipsoidal basalt to an ellipsoidal basalt in which, by 

 gradual transition, the grain has become considerably coarser; it is then an 

 ellipsoidal anamesite, if we use the terms basalt, anamesite, and dolerite to 

 express the degrees of coarseness of crystallization; it then grades into a 

 coarse-grained ellipsoidal dolerite, which in its turn grades into an even 

 coarser dolerite without marked ellipsoidal parting. Continuing, this same 

 sequence is gone over in reverse order, from the coarse, massive dolerite to 

 the fine-grained ellipsoidal basalt. The best place to get this complete 

 sequence is on the bare hills south of Moose Lake, along the section line 

 between sees. 32 and 33, T. 64 N., R. 9 W. Another place in which the 

 transition from the fine amygdaloidal ellipsoidal basalt to the massive 

 dolerite can be excellently seen is north of Long Lake. It is about 500 

 paces, or one-fourth mile, north of the southeast corner of sec. 9, T. 63 N., 

 R 12 W. 



Observations show that the amygdules are not the only features which 

 are common in the ellipsoids, as the ellipsoids are also commonly spherulitic."' 

 In fact, the spherulites have been observed only on exposures which show 

 a more or less perfect ellipsoidal parting. The best spherulites have been 

 seen where the ellipsoids are typically developed and show the following 



«Cole and Gregory, Quarterly Jour. Geol. See, Vol. XLVI, 1890, p. 311. 



