130 B.D. Irving—Hornblende of the Northwestern States. 
the chief part of the Glacial era, the earlier drift, or that from 
the northwestward, should be found in spots somewhere over the 
bottom of the valley, beneath the valley drift; and southeast- 
ward scratches as we ‘ift. ut none such occur. e 
bowlders of the upper current, or those from the northwestward, 
are mingled with the valley till, occurring within it, and on top of 
it. All evidence opposes the idea that it was brought in before 
the valley movement supplied the valley drift; and all facts ac 
cord with the explanation given that the bowlders of the upper 
glacier current sunk into the lower or valley current, and were 
‘deposited by the latter. Some of the bowlders taken from the 
region west of the valley in Massachusetts were carried 70 miles 
southward without going eastward more than half away across— 
the valley, or about ten miles. 
Art. XVIII.—Supplement to Paper on the ‘Paramorphic Origin 
of the Hornblende of the Crystalline Rocks of the Northwestern | 
by R. D. Irvine. . 
7 
States ;” by 
a 
resenting the crystalline schists, acid eruptives and basic yah 
tives of a region some 400 miles in length by 300 in width, 
and of three distinct geological systems, I have found no horn- 
blende that is not clearly, or very probably, secon 
i im the firs 
ing independently on the rocks of this region, it may tend to a 
prevent possible future misconceptions if I give a brief his- . 
torical account of the microscopic work hitherto done, and the 
bearing of the results on this question. This historical account 
was omitted from my ‘ae gee above referred to, through fear of 
making it too lengthy, it being supposed that lithologists 
be sufficiently cognizant of the facts. 
