September 2, 1S87.] 



SCIENCE. 



119 



cooling goes on from the surface, and is far more rapid than the 

 motion of the water to deeper layers : therefore ice is formed before 

 the cooled masses sink to the depth and are replaced by warmer ones. 



I can confirm Mr. Ashe's observation that the new ice frequently 

 forms first on projecting points. It seems to me that particles of 

 ice which have formed on the shore are driven by wind and waves 

 into the sea, and act as so many centres of congelation. As these 

 particles and small cakes are drifting before the wind, long, narrow 

 streamers are formed, each new opening being rapidly filled by new 

 ice. These narrow strips do not consolidate, but are driven to a 

 lee coast, or their motion is stopped in some other way. Then they 

 are pressed together, the small cakes are broken and overflowed by 

 ripples, the water freezes on top of them, and within a short time an 

 extensive field is formed consisting of numerous small cakes pressed 

 and piled upon one another, and cemented by the water that has 

 overflown them. Besides this kind of ice, which is formed while 

 the wind is blowing, smooth floes are formed in small bays during 

 calm weather. The latter, however, form the smaller portion of 

 Arctic ice. This process accounts for the great quantity of brine 

 contained in the new ice. The deeper laj'ers contain far less salt 

 than the surface ice, as the mechanical admixture of water takes 

 place on the surface only. The snow, on falling on this kind of ice, 

 forms a slush, as it melts in the brine oozing out of the ice. This 

 mixture freezes, and thus the thickness of the ice increases on the 

 upper and lower sides simultaneously. The different origins of the 

 layers of ice accounts for their different character. 



During the winter the ice undergoes remarkable changes. The 

 brine contained in ice of different depths is the more concentrated 

 the lower the temperature of the layer. It is probable that the 

 cavities between the ice-crystals are sufficient to effect a gradual 

 decrease in the concentration of the upper parts, which then begin 

 to freeze, and thus become drier. 



When in spring the ice begins to melt, it loses its salt rapidly, and 

 I observed in latitude 70° north, on the west coast of Baffin Bay, 

 that it had become entirely fresh about the end of June, the brine 

 being removed through the capillary cavities. 



A remarkable effect of mechanical action upon the dissipation of 

 the sea-water ice may be observed at places where rapid tides are 

 running. When the temperature of the air rises to about — 20° C. 

 ( — 4° F.), the ice becomes saturated with water, and is being worn 

 off at its lower side. It seems that the lower surface of the ice is 

 rough, consisting of ice-needles with isolated points. These are 

 broken off by the violent motion of the water, and thus by the fric- 

 tion of the broken pieces the volume of the ice-sheet is continually 

 being diminished at its lower side. In winter the same process 

 must be giing on, though not to so great an extent. Some places 

 of this kind are open throughout the winter. Their extent is chang- 

 ing according to the strength of the tides ; and during the spring- 

 tides ice of about fifteen or twenty centimetres thickness, which 

 was formed during the preceding neap-tide, is broken up and 

 pressed under the neighboring floe : consequently the thickness of 

 this ice would continually increase if it was not worn off at its lower 

 surface. In fact, the ice in such places is very treacherous and thin : 

 therefore it seems, that, according to the strength of the current, a 

 certain low temperature is required to resist its destructive influ- 

 ence. Below the layer which has this temperature the ice is satu- 

 rated with water and being worn off. 



Mr. Ashe touches upon another subject the explanation of which 

 seems to me insufficient. On steep coasts in the Arctic regions an 

 ice-wall is found attached to the rocks, and reaching from high- 

 water to low-water mark, gradually decreasing in thickness, and 

 having a vertical side. When the tide ebbs, the wet rocks are ex- 

 posed to the cold air, and of course are covered with a thin sheet of 

 ice. This process begins before the sea is frozen over, and, as the 

 water is still agitated by winds, the thickness of the layer formed 

 during a single tide is considerable. This process is going on 

 throughout the winter, and thus this ice-foot continues to increase 

 in width. At spring-tide its level is overflown by water, which 

 adds to its height. It is characteristic of this ice-foot that the un- 

 broken land-floe extends to its foot, a single crack separating the 

 two masses. Cliffs which are washed by water throughout the 

 winter have frequently no ice-foot at all. This shows that the floe 

 favors its formation. 



The ice on shores with a gradual slope is quite different. Here 

 it is not attached to the bottom, as Mr. Ashe's description would 

 imply, but originates in the following way. The ice which is 

 formed on the surface at high water strands during the ebb-tide,, 

 and its volume is increased by the freezing of the water left on the 

 beach. When the tide comes in again, the greater part of this ice 

 begins to float, increases in thickness, and strands again on the 

 rocks. By the repeated breaking of these masses on the rocks, the 

 water is frequently exposed to the air, freezes, and thus the thick- 

 ness of the ice is far more rapidly increasing than that of the un- 

 broken floe. It is continually growing on all sides, new material 

 being also added on the sides, and thus a heavy pressure results 

 which affects the neighboring parts of the floe, which is frequently- 

 pressed under the level of the sea, is overflown, and thus increases 

 in thickness. If the slope is sufficiently gentle, this part of the floe 

 strikes also the rocks at low water, and is added to the growino- 

 belt of grounded broken ice that surrounds the coast. Similar 

 forms of ice are found on mud-beaches, and I believe that such is 

 the origin of the unusually heavy mud-colored masses of Fox Basin, 

 which is known to be extremely shallow. 



The formation of the ice-foot which was described above is 

 similar in origin and appearance to the frozen freshets which in 

 winter form ice-walls that are firmly attached to the steep cliffs. 

 This proves that Mr. Ashe's explanation of this fact is not correct, 

 and that fresh water as well as sea-water may freeze firmly to the 

 ground. Dr. Franz Boas. 



New York, Aug. 19. 



The Geologists' Congress. 



Permit me to say a word concerning the generally fair and full 

 report, in Science, of the proceedings in Section E of the American 

 Association. By a typographical error, a clause in the conclusion 

 of the digest of the reporter on the Archcean is made to read 

 " American geologists will acquiesce in the recommendations of 

 the committee," etc. ' Congress,' not ' committee,' was the word 

 used. Again, " the recommendation that all pre-Cambrian rocks 

 should be called Archsean savors too much of pre-judgment, espe- 

 cially in view of the recent studies of Irving and Walcott." 



These studies, which have resulted in the theory called by Pro- 

 fessor Walcott, in his letter to the reporter, ' Prof. R. D. Irving's 

 view,' were very carefully considered in the body of the report. 

 The sentence above gives no idea of the entire recommendation ; of 

 how far it differs from the view of Irving, Chamberlin, Walcott, and 

 others ; nor of why it seems to best reconcile the conflicting views 

 expressed by American geologists, ist. The term ' Archsean ' as 

 originated by Dana received the unanimous suffrages of the Berlin 

 Congress, and, so far as the reporter could ascertain, has the in- 

 dorsement of a very large majority of American geologists as a 

 general term to cover all pre-Cambrian rocks. Irving would sepa- 

 rate these rocks into two divisions of equal rank : to the lower 

 (Laurentian) ' Archsean ' should be applied, the upper (separated 

 by a physical break from the first, and containing an unspecified 

 number of smaller breaks or unconformities) he would erect into a 

 new group of equal rank with Archsan in its new sense, and 

 would call it, after Chamberlin, ' Agnotozoic' He recognizes " great 

 unconformity between the Cambrian and the Agnotozoic, besides 

 which there are minor, though still quite extensive, unconformities 

 between the members of the Agnotozoic itself." It is evident, from 

 the tenor of all the views expressed on this proposed new division, 

 that its exact rank is not certainly understood. All who recognize 

 it believe that it has at least as high a rank as ' Paleozoic,' ' Meso- 

 zoic' etc., but none can yet affirm that it may not consist of several 

 such groups, divided by one or more of these ' extensive uncon- 

 formities.' In view of this fact, and also of the circumstance that 

 to a vast majority of geologists to-day the Archjean includes all 

 pre-Cambrian rocks, it was thought that the recommendation of the 

 reporter avoided, to the greatest degree, any pre-judgment of this 

 question. It is as follows : — 



" The division first in order of time shall have a rank of the first 

 order, and shall be called ' Archaean.' {a) It shall comprehend all 

 the rocks of origin anterior to the Cambrian, {b) The lowest sub- 

 division of the Archaean shall be called the ' Laurentian.' (c) A 

 division between the Laurentian and the Cambrian, provisionally 



