Sijnchronism of the Lake Superior Reriion. — Winchell. 209 
rock, or simply gabbro, embracing tlie crystalline apatites and 
the titanic iron ores of the country, and, as dependencies, 
certain marbles and quartzose gneisses with their graphite and 
non-titanic magnetites and a large variety of novel mineral 
species, protrudes itself upon our notice. That it should ap- 
pear in North America at so widely separated points, at essen- 
tially, if not precisely, the same time in the early history of 
the earth, is a remarkable event which calls for some explana- 
tion other than the ordinary reference to oceanic conditions. 
This great plutonic agitation appears to have been felt along 
a belt extending from southern New York northward through 
the Adirondacks, through Canada, appearing on the north 
shore of lake Huron, where coarse eruptives are mingled with 
the broken and subcrystalline strata of the "original Huron- 
ian," to lake Superior and the region of Duluth, occurring on 
both sides of the great basin. More recently a gabbro of sim- 
ilar character has been discovered about 120 miles still further 
west in Minnesota. How far southward along the Appala- 
chian fold this effect can be distinguished from that of other 
epochs of irruption and crystallization is unknown, but simi- 
lar gabbro rock has recently been announced in the vicinity 
of Philadelphia* and Baltimore. f The actual eruption of the 
characteristic labradorite-anorthosite rock may not have pre- 
vailed in all those regions throughout which, still, the cotem- 
porary folding and metamorphic changes were imprinted on 
the earlier rocks. In the latter effects this epoch may perhaps 
yet be identified over wide areas on the Appalachian moun- 
tains and its rocks may be found to extend much further 
northeastward toward the mouth of the St. Lawrence, and to 
be of the age of the rock in La])rador from which its cliief 
feldspar is named. 
Another lithological constant involved in the rocks of the 
Taconic from eastern New York and Vermont to northeastern 
Minnesota is the iron ore horizon which appears overlying the 
basal quartzyte of the Animikie. That tliis must have de- 
pended on oceanic causes inherent in the Taconic for its 
stratigraphic position as well as for its geographic extent, is 
*J. F. Kemp. On an occurrence of gabbro (noritei near Van Artsda- 
len's qU'iii'^S Bucks countv, Pennsylvania. Tians. N. V. Acad. Sci., 
vol. XII, March, 18L)3. 
jG. H. Williams. Bulletin 28, U. S. Gcol. Sur.. ISSC. 
