148 THE VERMILION IRON-BEARING DISTRICT. 



Other good exposures of spherulitic, ellipsoidal greenstones, in which four 

 or five rows of spherulites can be seen, occur in the northeast corner of 

 sec. 7, T. 63 N., R. 11 W. Perhaps even better ones can be seen south and 

 southeast of Jasper Lake, especially in sec. 6, T. 63 N., R. 9 W. Here 

 the hills are nearl)^ bare and exposures extend almost continuously from 

 the south shore of Jasper Lake eastward along the section line to the south 

 quarter post of sec. 6, T. 63 N., R. 11 W. 



These ellipsoidal or aa greenstones have been subjected to orogenic 

 movement, and when in the zone of fracture" they have been jointed, and 

 in places brecciation has also taken place. A different result followed 

 when the rocks were more deeply buried and subjected to great pressure, 

 which produced interesting structures that are in some places now 

 exposed at the surface. The ellipsoids then, instead of being fractured, 

 were mashed into disks, just as one could mash a lump of stiff dough into 

 a disk-shaped body. The cross section of such a mashed ellipsoidal 

 greenstone shows that the ellipsoids have enormously elongated axes, 

 approximately parallel to the direction of minimum pressure, and a 

 proportionally short one in the direction of greatest pressure. Various 

 stages of this deformation have been observed. In extreme cases these 

 rocks have a banded appearance, the material of the ellipsoids forming 

 bands of dense material alternating with other bands which consist of what 

 was the matrix between the ellipsoids. This rapid alternation of bands of 

 differing material — the bands derived from the matrix may be an inch and 

 a half in thickness, the bands from the ellipsoids being usually a little 

 thicker — very closely simzilates true bedding, and might very readily be 

 construed as such on a hasty examination. Especially might it be so taken 

 in cases where, as frequently happens, the exposures are only a few square 

 feet or at most a few square yards in area. If one had lai'ge areas of these 

 massive ellipsoids to study, however, the bands, if examined in detail, would 

 be found to be relatively short and to be made up of enormously elongated 

 lenses. Such large exposures are, however, rare. One of the best exposures 

 of rock of this sort is on the high ridge south of the exploring camp on 

 the south side of Moose Lake. The rock here is the typical spherulitic 

 ellipsoidal greenstone, and shows verj^ nearly clean exposures over an 



"Principles of pre-Cambrian geology, by C. B. Van Hise : Sixteenth Ann. Kept. U. S. Geol. Survey, 

 Pt. I, 1896, p. 696. 



I 



