April 6, 1883. 



SCIENCE. 



249 



sandstone ; this lava was partially denuded, and buried 

 under a conglomerate composed of its debris, mingled 

 with rhyolitic, trachytic, and granitic material. The 

 detritus was also buried under another lava-flow ; and 

 this alternating action went on, first with increasing 

 and then with diminishing eruptive activity, until the 

 western sandstones and conglomerates were reached, 

 which were laid down on the last lava-flow. It is 

 probable the lava came from fissure eruptions. Wher- 

 ever the detritus was deposited on the lava, whether 

 within the trappean belt or on its western side, de- 

 nvidation has taken place, and fragments of the trap 

 (melaphyr and diabase)have been enclosed in the over- 

 lying detritus. Unconformability would, of course, 

 thus exist, and the writer has figured such a case ; but 

 it is the unconformability that always exists when lava 

 flows on a shore, and is subjected to the denuding ac- 

 tion of the waves, and proves nothing regarding the 

 geological age. 



The evidence which Irving claims has been ignored, 

 and which he says is "proof absolute that the Ke- 

 weenawan [copper-bearing rocks] series belongs below 

 the base [Potsdam] of the paleozoic column of the 

 Mississippi" {Geol. Wise, iii. 23), is principally the 

 finding of a trappean rock at Taylor's Falls, against 

 which rest sandstone and shales holding fragments 

 of the trap and primordial fossils. Excepting the 

 fossils, these are exactly the conditions which are 

 found, and which ought to be found, within the 

 copper-bearing belt, and on its western side; and 

 it proves nothing regarding geological age, but only 

 sequence of time. If such evidence as this is ' proof 

 absolute' of distinct geological age, then there is 

 proof absolute that there are as many different geo- 

 logical formations in the copper-bearing rocks as there 

 are detrital beds enclosed in the traps, and proof that 

 the last lava-flow of any active volcano, reaching the 

 sea, is separated by a distinct age and ' immense un- 

 conformity' from the detritus deposited upon it be- 

 fore it is hardly cold. Unconformity of itself proves 

 nothing, unless both formations are sedimentary ; for 

 an eruptive rock cannot, from the very nature of the 

 case, be conformable, in the true sense, with any thing. 

 The relations that the old basaltic lavas have, accord- 

 ing to Irving, to the western sandstone, are exactly 

 what they ought to have from their origin, as shown 

 thirty-three years ago. 



Again : according to the Wisconsin geologists, the 

 Taylor' s-f alls trap is fifteen miles from any other so- 

 called copper-bearing rocks, and may as well be an 

 azoic rock; for similar ones have been collected by 

 the writer in the granite of the Marquette azoic dis- 

 trict. If it is referred to the copper rocks on litho- 

 logical grounds, the same argument could be used to 

 unite with this series a large part of the basaltic traps 

 the world over. The resemblance between them is, 

 in the writer's opinion, that which any two basaltic 

 lava-flows or dikes have wherever they may have been 

 extruded. 



The writer has shown that the first trap on the east 

 overflowed and indurated the eastern sandstone ; and 

 he collected specimens showing the induration, the 

 trap, and the trappean detritus in the overlying con- 

 glomerate. Therefore Irving's statements, that the 

 eastern sandstone unconformably overlies the trap, 

 and that no trappean detritus occurs in the fragmental 

 rocks, are jncorrect; and the published evidence was 

 in his hands several years ago. Irving is mistaken 

 when he says that all the geologists who approached 

 the question from the east felt baffled, as the writ- 

 ings of Foster and Whitney, Selwyn, or myself, give 

 no indications of the kind. It may be mentioned, 

 that in 1850 Foster and AVhitney showed that a fault 



existed along part, at least, of the eastern, side of the 

 traps, and that the Bohemian range was a later pro- 

 trusion. This evidence will explain the apparent 

 unconformity of the traps with the eastern sand- 

 stone observed in some places. 



For a fuller discussion of the copper-bearing rocks 

 and allied formations, together with the literature 

 down to ISSO, the writer would refer to the bulletin 

 of this museum, vol. vii. pp. 1-1.57. 



M. E. Wadsworth. 



Mnsoura of comp. zool., Cambridge, 

 Mass., March 15, 1883. 



Domestic ducks that fly abroad like pigeons. 



In response to Mr. Storer's note under the above 

 heading (Science, No. 3), I would state that in my 

 boyhood I lived on a' plantation in Liberty County, 

 Ga., on which there were a great many domesticated 

 ducks, both mallards and musk-ducks. Many of these 

 latter belonged to the negroes, and were tended with 

 but little care. Near by the negro village there was a 

 swamp full of large trees, and often covered with 

 water. A considerable portion of the swamp was 

 cleared, and annually planted in rice; but many dead 

 cypress (Taxodium) trees still remained standing. 

 This swamp was a favorite resort for wild ducks of 

 all kinds, especially mallards, teal, and summer ducks 

 (wood-ducks). Many domesticated musk-ducks, es- 

 pecially those belonging to the negroes, flew abroad 

 every morning, remained in the swamp <one to two 

 miles distant) all day, and returned at night. Some 

 of them built their nests and reared their young in 

 the swamp, though they never became thoroughly- 

 wild. 



I never observed this habit, except in the musk- 

 duck. The reason, I think, is plain. In shape, in gait, 

 in flight, and in habits, the musk-duck is very similar 

 to the wood-duck (sponsa). Like the latter, it walks 

 with freer step, it rises, flies, and alights with gi-eater 

 ease and grace, than other species, because the wings 

 are broader and rounder. Like the wood-duck, also, 

 it alights on trees. The dead cypress-trees were a 

 favorite resting-place for the musk-ducks. Like the 

 wood-duck, too, it builds its nest on trees or stumps, 

 and takes down the young when hatched. I have 

 never known the musk-duck to build on the tops of 

 tall cypresses, like the wood-duck, but often on the 

 tops of hollow stumps fifteen to twenty feet high. 



Joseph LeConte. 

 Berkeley, Cal., Mai-ch 10. 



Apparent attractions and repulsions of small 

 floating bodies. 



To obviate possible misunderstandings, it may be 

 proper for me to make a few remarks in relation to 

 'E. H. H.'s' antique (Science, i., p. 43) on my 

 article (Amer. journ. sa., Dec, 1882) on the above 

 phenomena. 



I am to blame for whatever ambiguity attaches to 

 the use of the term 'tension' as applied to the expla- 

 nation of these phenomena. In one instance (that 

 cited) I inadvertently used the expression 'superior 

 tension' instead of ' superior /o)-ce.' But inasmuch 

 as in the formal announcement of the capillary prin- 

 ciple — which is applied to the case in question, ami 

 also in the preceding as well as the succeeding context 

 — it is very clearly indicated that the effective capil- 

 lary forces (and not the surface-tension) are regarded 

 as inversely proportional to the radii of curvature of 

 the meniscuses, few physicists will, I trust, be misled 

 by the expression. 



He does not admit "that a liquid film tends to 

 draw a solid, to which it is attached, toward the centre 



