124 The American Geologist. February, 1900 
put into definite form, expressed in mathematical terms and presented 
diagrammatically by a plate of contours showing the variation of grain 
at dififerent distances from a cooling surface. In making application of 
the principles deduced the author chooses the augite of the ophytes, 
and, making measurements of numerous augites as they appear in thin 
section under the microscope, he found, practically, that in flow, 
masses the increase in the size of the augites continues from the mar- 
gin to the center of the mass; that the area of a cross-section of a 
grain varies as the square of the distance of the latter from 
the margin; that the area of a cross-section of a grain varies 
directly as the slowness of cooling, and that the linear dimensions of 
the augite patches are directly as the distance from the margin; but 
that in Keweenawan intrusive rocks the size of the grain increases 
from margin toward the centre rapidly for a certain distance, re- 
mains uniform through a central belt and diminishes again on ap- 
proaching the opposite side of the mass; and these truths are ap- 
plied also to the feldspars, the olivines and the iron oxides, though 
with less conclusive result. 
7. The direction of the general ice movement of the glacial epoch 
was from the northeast, or nearly in the direction of the strike of the 
rock ridges, but a little more from the east, so that the grooves run 
slantingly slowly up the ridges. 
8. The highest terrace of the lake is 490-498 feet above the lake, 
the greatest hight of the island being only 500 feet, with several ter- 
races at lower levels. 
9. Micropegmatyte is considered an original structure when seen 
in the diabases cutting the iron-bearing rocks, especially in that of 
Lighthouse ppint, at Marquette. 
Dr. Hubbard's discussion of the felsytes is equally interesting and 
important, and is more systematically and smoothly presented. Dr. 
Hubbard first gives a lot of details of observation at Schlatter lake, 
At Bare hill, Mt. Houghton, and other adjacent localities, mainly per- 
taining to the felsyte and its structural relations. From these he de- 
duces sorne interesting conclusions, and then proceeds to give some- 
new facts and interpretations as to the general structure of Keweenaw 
point. From his report we can summarize briefly the following main 
results, some of which, while considered still as hypothetical by the 
author, he presents as the most probable explanation of the facts. 
1. Keweenaw point consists, at least eastward from Allonez gap, 
of two principal trap ridges, the northern being known as "the green- 
stone," and the southern as the "Bohemian range," the southern ex- 
tending to the extremity of Keweenaw point, and its rocks dipping 
northward below the greenstone range. 
2. The acid or felsitic rocks prevail in the bottom of the Bohe- 
mian range, both as conglomerates and as instrusives and flows. 
3. In several instances, notably at Fish Cove Knob, West Pond, 
Bare hill, etc,, the felsyte as an intrusive amongst the basic traps is 
plainly later than the tr^ps; but they also appear to have formed inde^ 
