5 et 
Geological Notes. 389 
region, so far as yet known. Possibly it may have been 
removed by denudation before or during the Huronian age, 
or it may have assumed different mineral characters which 
may have caused it to be referred to the so-called Kewatin 
or Lower Huronian group. 
2.—The Most Ancient Fishes. 
Walcott has now found, and showed me when in Washing- 
ton, large portions of the armour of a Placoganoid from 
the Siluro-Cambrian of Colorado. These fragments seem 
completely to remove any doubts as to the nature of the 
detached plates previously found. They have not as yet 
been described ; but would seem to indicate a type not very 
remote from some Upper Silurian and Devonian genera. 
3.—Comparison of Existing and Pleistocene Glaciers. 
An interesting and thoughtful paper, by Warren Upham, 
has just appeared,* in which he institutes a comparison 
between “‘ Pleistocene and Present Ice-sheets.” The present 
ice-sheets are stated to be four. (1.) The Antarctic or that 
which fringes the Antarctic continent and is probably bet- 
ter entitled to the name than any other; but which differs 
from the supposed ce-sheets of the Pleistocene in fronting 
on the sea and discharging all its produce as floating ice. — 
In this, however, it certainly, resembles many of the great 
local glaciers of the Pleistocene. (2.) The great nevé of 
Greenland, which however discharges by local glaciers 
and these open on the sea. (3.) The Malaspina glacier of 
Alaska, evidently a local glacier of no great magnitude, 
though presenting some exceptional features. (4.) The 
Muir glacier of Alaska, also a local glacier, but perhaps, 
like the Malaspina, showing some features illustrative of 
local Pleistocene glaciers. 
In the “conferences and comparisons,’’ however, the facts 
detailed in the earlier part of the paper are placed in com- 
parison with postulates respecting the Pleistocene which 
are incapable of proof. (1.) Itis taken for granted that 
* Bulletin Geol. Society of America, March 24, 1893. 
