ELY GREENSTONE. 147 



relations to these ellipsoids. The smallest spherulites occupy the extreme 

 outside of the ellipsoids. From the outside they increase in size toward 

 the center, where, if the rock is there spherulitic at all, the largest 

 spherulites are developed. Sometimes the development of the magma 

 into a spherulitic rock did not reach entirely to the center, which is then 

 developed as a massive dolerite of normal chai-acter. It is very noticeable 

 that while the spherulites occur in the very fine-grained lavas they are 

 apparently equally common in some of the more coarsely crystalized forms 

 when these phases are ellipsoidal. The spherulitic and amygdaloidal 

 structures sometimes occur together, but most commonly they are not 

 developed in the same rock. Apparently the presence of one does not 

 altogether preclude the existence of the other, although it amounts very 

 nearly to this. Thus, in passing over the particular section through the 

 ellipsoidal amygdaloidal lavas, which was noted above as occurring north 

 of Long Lake, we find that the amygdaloidal ellipsoidal fine-grained lava 

 is first nonspherulitic. Soon, however, the spherulites begin to appear and 

 gradually increase in importance, the amygdules decreasing correspondingly 

 in quantity and the grain of the matrix between the spherulites increasing 

 also in size. The spherulites, however, are wanting in the coarsest non- 

 ellipsoidal phases of the lava. The arrangement of the spherulites in 

 concenti'ic circles made up of spherulites of larger and larger size as the 

 center is approached shows, as does the concentric arrangement of 

 amygdules in the ellipsoids, that each ellipsoid must be reckoned with as 

 a unit. Observations show that small spherulites occur on the outside of 

 a spherulitic mass, where crystallization continues for only a short time, 

 while the larger spherulites, requiring proportionally a longer period for 

 their formation, occur deeper down in the rock. 



Magnificent exposures of these spherulitic ellipsoidal greenstones 

 occur on the hills north of Long Lake for the greater jjortion of the distance 

 between this lake and Bass Lake, in sees. 9 and 10, T. 63 N., R. 12 W. 

 One of the finest exposures seen was that occurring on the high hill about 

 500 paces south of the meander corner on the shore of Bass Lake. The 

 illustration presented in B of PI. IV is made from a photograph of this 

 exposure and shows the spherulitic character of the ellipsoids; the eight 

 spots in the photograph are the spherulites. The somewhat schistose, 

 brecciated matrix between the ellipsoids can also be seen in the illustration. 



