Febeuaey 14, 1896.] 



SCIENCE. 



251 



of sphagnum, 5 to 8 inches thick, as porous and 

 absorbent as a sponge. The stem and leaves of 

 sphagnum have a peculiar porous structure, 

 through which a constant flow of water is car- 

 ried up and poured out to evaporate on the 

 surface. Thus by constant evaporation, the 

 plant and its surrounding atmosphere are kept 

 «old. Ice was found under the sphagnum in one 

 of these swamps as late as May 10, although the 

 preceding winter had been mild and the snow 

 had all disappeared by the middle of March. 

 A number of small shrews (Sorex personatus), 

 a boreal species of a boreal genus, were taken 

 in one of these swamps, some being caught in 

 traps resting on ice. The star-nosed mole, 

 another boreal mammal, also occurs in some of 

 these swamps, and the varying hare {Lepus 

 americanus) was formerly common. 



Evidently these boreal species of plants and 

 animals are retained in the Southern swamps 

 by the low temperature produced by evapora- 

 tion from the sphagnum. F. A. LucAS, 



Secretary. 



GEOLOGICAL CONFERENCE OF HARVARD UNI- 

 VERSITY, JANUARY 21, 189(3. 



On the Origin of the Copper Deposits of Keweenaiv 



Point: By Prof. H. L. Smyth. 



After a brief review of the character and struc- 

 ture of the rocks of the Keweenawan Series, 

 and the geological and geographical distribu- 

 tion of copper in them, the author pointed out 

 the close genetic connection between the three 

 forms of occurrence of copper in this district. 

 The amygdaloid and conglomerate ' floors ' in 

 the vein mines are essentially the same except 

 in scale, as the greater impregnated and re- 

 placed amygdaloids and conglomerates. From 

 this consideration all would date from the time 

 of formation of the fissures of the vein mines ; 

 this was probably the time of general tilting, and 

 long subsequent to the formation of the lower 

 flows and conglomerates. 



Pumpelly worked out many years ago a para- 

 genetic series among the mineral associates of 

 the copper ; this series cleaves along a chemical 

 line. The earlier minerals, which preceded the 

 copper, are chlorite mainly, with certain other 

 non-alkaline hydrous silicates ; the latter are 

 alkaline, and are close contemporaries of the 



copper. Among them are apophyllite (a fluorine 

 mineral), and datolite (a boron mineral). Calcite 

 is abundant through the whole series. 



The author pointed out that from the consid- 

 eration of the conditions of formation of the 

 separate flows, with their subordinate inter- 

 calated conglomerates, each after consolidation 

 was immediately subjected to the action of 

 meteoric waters. Afterwards, by slow subsi- 

 dence, each bed would eventually sink beneath 

 their reach. The minerals of the first division 

 of Pumpelly's series, essentially weathering 

 products, belong to the successive periods of 

 exposure of individual beds. The observed 

 progress of alteration, from top to bottom in 

 each individual bed, accords with this view, as 

 do also the non-alkaline alteration products. 



Afterwards came the northerly and north- 

 westerly tilting, and the formation and filling 

 of the fissures, and the impregnation and partial 

 replacement of the amygdaloids and conglom- 

 erates. The new minerals of this period are 

 sharply separated from the alteration products 

 of the first (which they often replace) by their 

 richness in alkalis, and the presence of fluorine 

 and boron. The two periods, therefore, are 

 far separated in time as well as by the character 

 of the chemical agents at work, and do not, as 

 Pumpelly supposed, represent a continuous 

 march of alteration. 



The author then discussed the more immedi- 

 ate questions of origin, and concluded that 

 neither Pumpelly's view, that the copper had 

 been brought down from the sandstones of the 

 upper division of the series, nor Wadsworth's, 

 that it had come from the lava-flows themselves, 

 was probable. On the other hand, the mineral 

 associates of the copper, the time of formation, 

 and, in the case of the veins, the evident arrest 

 of the copper-bearing solutions below the rela- 

 tively impervious greenstone, all pointed to a 

 deep-seated source and to ascending solutions 

 as the transporting agent. 



As to the precipitating agent, the author 

 could not accept the view that it was electro- 

 lytic in its nature, because the deposition was 

 manifestly accompanied in so many cases by the 

 chemical destruction of the cathode. It was 

 concluded that in spite of lack of confirmation 

 by laboratory experiment, no theory so well ex- 



