252 The American Geologist. April, 1891 
From 1868 to 188G no special mention was made of the white 
limestones. The question was practically settled. In 188G how- 
ever, Dr. Britton, in his classification of the rocks of New Jersey, 
showed clearly that the idea of the Archaean age of these lime- 
stones had grown in strength with the lapse of years. In this re- 
port, "State Geological Survey, 1886," pp. 77 to 83, he again 
groups the crystalline limestones in the Archaean. His grounds 
for this are not new : — interstratification with gneisses and con- 
formability. 
This brings the history of the question as to the age of the 
white limestones of the Northwest border up to date, so far as 
New Jerse}^ is concerned. It will be seen, I think without doubt, 
that there is absolutel}* no proof offered which seems to establish 
the opinion that these limestones are Archaean ; on the other hand, 
Prof. Rogers recorded enough of evidence to establish their post 
Archaean age, or at least to have kept the question open. 
In the comments which I have made I have endeavored to point 
out the errors of the older writers as well as to again record their 
more valid observations. 
THE MOVEMENT OF ICE ON MINNESOTA LAKES. 
By E. H. Atwood, St. Cloud, Minn. 
The present winter has been a favorable one for studying the 
causes of the ice movement upon the numerous lakes in Minne- 
sota. Residents of this state are familiar with the sight of the 
upheavals of the ice upon our lakes, and to those dwelling in the 
vicinity of lakes the roaring of the ice during the changes of 
temperature is of so frequent occurrence that but little notice is 
taken of it. The absence of snow upon the ice exposes it to the 
weather, and as it is as sensitive to changes of temperature as a 
thermometer the present winter has caused an unusual movement. 
There are but few if any lakes in Minnesota where the conditions 
are so favorable for studying the ice movement in all its different 
relations as can be found upon Pearl lake, situated in Maine 
Prairie township. A recent visit to that beautiful sheet of water 
found the ice crowding with tremendous force upon the southern 
shore. Along this shore are situated numerous springs where 
the water oozes up through the gravelly bottom, which prevents 
the ice from freezing to the bottom and sides. As there are no- 
