Striation of Rocks by River Ice.— Todd. 397 
may striate, cases are rare where they have been shown to do 
such work. 
Croll, in ‘‘Climate and Time,” pp. 272-279, reviewing the ob- 
servations of Campbell and others about the gulf of St. Law- 
rence at various points, and along the St. Lawrence and Ottawa 
rivers, concludes that floating ice does not striate. The only 
case he admits is one seen by Lyell at cape Blomidon, on the 
west side of the Basin of Mines, in a tidal channel where the 
conditions were similar, as we understand, to those in a river. 
Lyell, after searching diligently along the river below Quebec 
and at the falls of Montmorenci, concludes as follows: <‘‘In none 
of these places were any long, straight grooves observable, and I 
feel persuaded that any degree of freedom of motion in the rocky 
fragments forced along by small pieces of ice, or by flood of 
water, would be quite incompatible with the mechanical effects 
exhibited in what are called glacial grooves.”’ (Travels in North 
America, 1841-2, Vol. 2, p. 115). From his method of speak- 
ing, it seems that he may have found striz, but he was not so 
much endeavoring to decide whether the ice scratched the rocks, 
as to determine if it could imitate so-called glacial grooving. 
Chamberlin, in his Rock Scorings of the Great Ice Invasion, 
doubtfully refers some scratches in western New York, to the 
agency of ice-bergs. (7th Annual U. S. G. S., p-166). 
Little has been published, so far as the writer has (liscovered, 
on striation by floating ice, and still less about the action of river- 
ice. It has been his privilege to gather several interesting facts 
which have the greater importance because of their rarity. 
Ten years ago, at Running Water, 8. D., I first saw striz on 
chalk-stone a few feet above low water in the Missouri, so situ- 
ated that they could not be referred to glacial action, and to nothing 
ancient. The scratches were some of them 10 inches long, and 
bore 8. 73° E. They are on the north side of the river at the 
foot of cliffs above the landing. 
A few seasons after, I found unusual scratches among the 
many referred to glacial action, near Sioux Falls, Dak. They 
were deeper and rougher, with tapering ends and upon a boss of 
rock, apparently eroded from the south instead of the north. 
They were only a few feet above the present Big Sioux, a few 
rods distant. The longest were about 10 inches long, their direc- 
tion, N. 57° W., ¢. e., parallel with the course of the river, 
