862 The American Geologist. June, 1892 
rounded grains of quartz. ‘The microscopist makes his rejoinder 
that these remnants of stratification are illusive, due to dynamic 
metamorphism, and the quartz grains are of secondary origin. 
He further cites, as evidence of dynamic agencies in the origina- 
tion of those structures, the semi-decayed and broken condition 
of the other minerals. There are curious fractures in some of the 
mineral grains. They appear to be ‘‘streamed”’ out in the direc- 
tion of the schistosity. The feldspars are saussuritized, the horn- 
blendes are chloritized, the augites are converted by a well known 
alteration to hornblendes, the micas are hydrated and the men- 
accanite is changed to leucoxene. A dynamic metamorphism has 
produced a degradational change throughout the whole rock. 
This indicates that while the materials had originally unquestion- 
ably an eruptive origin, as denoted by their identity with other 
changed known eruptive minerals, they have been subjected to 
some grand force or forces of pressure and shearing, which lave 
wrought a profound alteration in them, bringing them a step, or 
a long march, toward decay and disintegration. The microscop- 
ist admits that his well-known and infallible guides are wanting. 
He sees nothing, or very little, of the ‘‘diabasic structure,”’ and 
the freshly crystalline interlocking of the constituent grains which 
characterizes an unquestioned eruptive rock, is almost entirely 
wanting. His title therefore, as it is not based on characters 
which known plutonic rocks possess, but on others which he as- 
sumes to be due to another and a later cause, is defective, and he 
has to admit it. If the features which the interior of the rock 
exhibits can. be ascribed to neptunic forces, as claimed by his 
opponent, the case is still a drawn game, unless there are inherent 
faults in the reasoning of one or the other—such that they can 
be pointed out and demonstrated. 
The purpose of the foregoing is to introduce a peculiar feature 
seen by the writer at Ely, on the Vermilion iron range, in Min- 
nesota. The country rock here is the characteristic greenstone of 
the region, massive, shapeless, rather light-colored, embracing 
scattered grains of free quartz so as to present sometimes a rough 
and harsh exterior on weathering, and having a gradual transition 
northward across the formation, first into a green schist, then into 
graywacke and lastly into a sericitic schist. With this transition 
there is developed a sedimentary structure which in its final con- 
dition is undeniable, the schist element becoming interbedded 
