202 The American Geologist. April, is97 
not to be considered as unimportant from an economic point 
of view. The most interesting opportunity for studying the 
acid series is afforded b^' the isolated peaks west of the Mag- 
dalena range proper, as in Magdalena and Elephant mountains 
which are parts of the great flows above indicated. 
The large mountains forming the nuclens of the range, pre- 
eminently Big Haldy and Timber peaks, are also volcanic, and 
although capi)pd with acid rock, occup}' the place of an old 
andesite eruption. The latter occupies the east side of the 
main range southwest of theclilfs of Water canon, and forms 
the country rock in which the gold segregation has oc- 
curred. 
It is jierhaps of more geological than economic interest to 
determine the age of the dykes of acid matter which, by in- 
tersecting the andesite, have provided the conditions for ore 
concentration in this district. The results of a brief study of 
the field seem to suggest that the acid intrusives are of the 
same age as the later t]ows above described. The gold seems, 
how(;ver, to be derived fi"om the andesite so that the ore is 
chiefly in selvages or brecciated margins rather than uniform- 
ly distributed in the quartz. A thorough petrographic study 
of the region has been begun but would not be admissible 
here. 
Enough has been said to indicate that a careful geological 
survey of the region would have important bearings on the 
economic development of the mineral resources. 
'I'hrougout the entire region so far as studied, there is no 
important exception to the rule that gold is segregated along 
(u:)ntacts of acid rocks with basic intrusives or the converse. 
Andesite is preeminently the gold-bearing countr3^ rock. 
VALLEY GLACIERS OF THE UPPER NUGSUAK 
PENINSULA, GREENLAND. 
Hy Balph S. TAPa;. Itliaca. N . Y. 
Valley Glaciers of Greoilaiid. Passing along the Green- 
land coast, one is almost constantly in sight of valley glaciers. 
Some of these are tongues from the great ice cap, but many 
are furnished with their supply from local snow fields. These 
are particularly abundant in the Vaigat straits and in Umenak 
fjord Here one sees every gradation between the large, well 
(icfined glacier, tei minating in the sea, and mere snow banks. 
