212 Correspondence. 
These observations on the joint action of river-ice and coast ice, on a 
very gently shelving shore, are worthy of record, as we have so few ob- 
servations, compared with the vast area of high latitudes, wherein the 
coast-ice is playing a most important part as a geological agent. 
The observations in Lapland, first cited, are of extraordinary interest; 
as herein is an agent, capable of effecting a greater amount of surface 
erosion, than ice in any other form; and the catastrophe at Kerschkaranza, 
seems to be more phenomenal than even those recorded by Sir George 
Nares, off the Grinnell coast; but this is probably owing to our igno- 
rance of the uninhabited ice-bound coasts of arctic lands. 
University of Georgia, Athens, Ga., Dec. 26, 1888. j, w". Spencek. 
Two Systems Confounded in the Huronian. In the Quarterly Jour- 
nal of the Geological Society for February 1, 1888, appears an important 
communication from professor T. G. Bonney which I have only recently 
found time to read with due attention. I wish now to make a note upon 
it The communication is entitled, "Notes on a part of the Huronian 
series in the neighborhood of Sudbury, (Canada)." Professor Bonney, 
passing off the gneisses of recognized Laurentian age, begins his investiga- 
tions on rocks supposed to be Huronian, and extends his studies westward 
more than fifty-nine miles beyond Sudbury — though most of his studies 
lie within two miles of Sudbury. The first rock encountered "is mainly 
composed of quartz and feldspar, with but little mica, though occasional 
thinnish bands of a fissile mica-schist occur. It is much jointed, and ap- 
pears to have a fiaggy bedding, reminding me," he says, "in its general 
aspect, of parts of the Highland 'eastern gneiss' in Glen Docherty, (that is 
where the crushing is less conspicuous) or of the schistose series on the 
south side of Perth Kobla, Anglesey". This zone is less than a mile wide» 
when "outcrops of a rock distinctly fragmental are exposed". A dark 
quartzose rock is observed west of Sudbury, and this grows more coarsely 
fragmental —the "fragments now showing very distinctly on a weathered 
surface, by a slight bleaching, some looking rather like a felsite, others 
like a holocrystalline ( ?gneissose) rock." Next comes a coarse breccia, 
looking rather like an agglomerate — the matrix a more or less fine-grained 
quartzite. Then follows a quartzite without fragments, and then another 
group of fragmental rocks, slightly reddish-gray, resembling a micro- 
granulite with dark green spots, and these include "gneissose and schistose 
rocks, and a greenstone, or possibly chlorite schist." Professor Bonney 
erroneously, I suspect, suggests that these may be Logan's "slate con- 
glomerate," though he leaves the matter undecided. This belt of eastern 
(or lower) "Huronian" rocks is obviously distinct, he says, from the 
Laurentian ; by which I understand that the mica-schists mentioned are 
sufiiciently distinct from the older gneisses. These older Huronian "rocks 
ure seen under the microscope to consist chiefly of quartz, feldspar and a 
brownish mica." "The rock certainly exhibits a fragmental structure 
with secondary reconstruction." 
After this, but still within two miles of Sudbury, the character of the 
geology plainly changes. The rocks are grouped as A. Quartzites — ordi- 
