304 THE CANADIAN NATURALIST. [-^^g« 



no uncommon occurrence for the anchors of the nets of a " seal- 

 fishery " on the north shore of the Gulf of St. Lawrence to be 

 frozen to the bottom at the depth of from thirty to sixty feet ; 

 and when anchors are then raised, they bring with them frozen 

 masses of sand. But it i> in rapid rivers that the formation of 

 anchor-ice is most remarkable, and most effective in excavating 

 these beds. It forms on the beds of rivers above the head of a 

 rapid, and frequently bursts up with a load of frozen mud or 

 shinde, or slabs of rocks, which it has torn from the bottom. This 

 phenomenon is witnessed every winter in the valley of the St. 

 Lawrence ; but it is best observed after a prolonged term of cold, 

 when the thermometer indicates a temperature considerably below 

 zero. Anchor-ice has only been observed, as far as my knowledge 

 of the subject goes, in rapid currents in open water; and the sud- 

 den and apparently inexplicable rise of the St. Lawrence during 

 extreme cold is most probably due to this cause.^ It is not diffi- 

 cult to see how the rivers issuing from beneath the precipitous 

 walls of glaciers, as described by Dr. Eink, may rapidly excavate 

 deep channels by means of anchor-ice, to be widened by the sub- 

 sequent operations of the glacier itself. Nor is it improbable that 

 by this means a glacier in very cold climates may increase from the 

 bottom upwards with a load of frozen mud and fragments of rock, 

 particularly near its base, when that does not meet the open sea. 

 The great lakes of North America, including Lake Winnipeg, are 

 excavated on the edges of the fossiliferous rock-basins ; and these 

 lakes may represent the boundary of a glacial mass similar to that 

 which now covers Greenland. — From the Journal af the Geological 

 Society. 



DESCRIPTION OF TWO AMERICAN SPONGES. 



By Dr. J. S. Bowerbank, F.R.S., &c. 



1. Tethea hispida^ Bowerbank. 



Sponge sessile. Surface strongly and thickly hispid. Oscul^ 

 and pores inconspicuous ? Dermis abundantly spiculous ; spicula 

 disposed at right angles to the surfice, uniformly crowded 

 together ; super-fusiformi, sub-ovo-spinulatc, very minute ; form- 

 ing a secondary series of defensive spicula. Primary series of 

 defensive spicula super-fusiformi-acuate or sub-ovo-spinulate, very 

 large and long. Skeleton spicula super-fusiformi-acuate and sub- 



* See "Notes on Anchor-Ice," by T. C. Keefer, C.E., Canadian Jour- 

 nal, new series, vol. vii, p. 173, (1862). 



