1 66 



SCIENCE. 



[Vol. X. No. 243 



LETTERS TO THE EDITOR. 



*^,* The aii37ttion of scientific jtzen is called to the advantages of the correspondence 

 columns ofiSciuacKfior placing promptly on record brief preliminary notices of 

 their investigations. Twenty copies of the number containing his communication 

 will be furnished free to any correspottdent on request. 



The editor -will be glad to publish any queries consonant with the character of 

 thejournal. 



Correspondents are requested to be as brief as possible. The writer s najtie is 

 in all cases required as proof of good faith. 



The Keweenawan System. 



The geologists interested in the discussions that have taken 

 place during the past eight years, concerning the relations of the 

 Eastern sandstone to the copper-bearing rocks of Keweenaw 

 Point, will remember that one of the important localities showing 

 that relation is situated on the Hungarian River. In company with 

 James Osborne, F.G.S., superintendent of the Rio Tinto mines in 

 Huelva, Spain, and William Beer of the Osceola Mine, I have re- 

 visited this locality. Owing to some changes in the bed of the 

 stream, we are able to trace continuously the unchanged Eastern 

 sandstone into the sandstone which has been baked and indurated 

 by the old lava-flow, and this baked sandstone into the lava-flow 

 or melaphyr itself, all forming a continuous exposed surface. 

 There is no fault or plane of separation between the sandstone 

 and trap, but the two are welded together into one mass. We 

 procured hand specimens, which in one piece show the contact 

 of the so-called ' Keweenawan ' system with the Eastern sandstone. 

 The contact is that made by a lava-flow with an underlying 

 sandstone, and is the same as the contacts so often observed 

 within the copper-bearing series, while the sandstone is observed 

 in situ to pass beneath the melaphyr. It is my purpose to uncover 

 the contact junction still further, and to publish in time a paper 

 giving sections and detailing results at this and other localities at 

 which the contact has been observed. The above observations 

 sustain fully those made by myself in 1879; and in this case it 

 would seem to forever settle, beyond any possibility of doubt, that 

 the Keweenawan system and the Eastern sandstone are one and 

 the same continuous geological formation, but with the copper- 

 bearing rocks younger in point of time than the sandstone. 



M. E. Wadsworth. 



ilichigan Mining School, Houghton, Mich., Sept. ig. 



larity in color of the spots and the larvae are a protection to the 

 latter. Herbert Osborn. 



Zool. Lab. Agric. Coll., Ames, lo., Sept. 20. 



Cause of the Purple Coloring of Pigweed-Leaves. 



During a number of years past I have frequently been struck 

 by a prevalent purple coloring of patches in the leaves of pigweed 

 {Ckenopodiuni album), the cause of which did not appear in any 

 surrounding conditions, and up to this summer it has remained to 

 me a mystery. A few weeks ago, howe\'er, while examining pig- 

 weed in search more particularly of plant-lice and leaf-miners, I 

 again noticed the leaf-coloring, and, upon turning up some of the 

 colored leaves, found on some of them larvae of a leaf-hopper having 

 the same shade of purple as the colored spots on the leaves. Further 

 examination brought to light more of the larvas, always on the 

 under surface of the leaf, and within one of the colored spots. 

 Some of the spots were found without any larvae visible, indicating 

 that they travel about more or less, or that they had been disturbed 

 and had made use of their legs to get out of the way. A few days 

 later (July 25) I examined plants in another locality similarly af- 

 fected, and found, as before, the colored larvse associated with the 

 spots. On one leaf, I found close by the cast-off pupa-skin, which 

 still retained enough of the markings to show its relation to the larvse 

 (an adult), which, on comparison, proved to be the Thainnotettix 

 seviimcdiis of Say, — a species rather common throughout the 

 country, but which, so far as I can find, has never been mentioned 

 in connection with its food-habits or larval life. No such coloring 

 results from the presence of plant-lice or other insects on the 

 same plant, and it seems quite certain that we may consider this 

 species as the cause of the peculiar phenomenon. I am not aware 

 that any explanation has previously been given. What kind of 

 secretion is injected into the leaf by the insect, when puncturing it 

 to obtain its food, and how that acts to change the color in the 

 plant-cells, are still open questions. It is evident that the simi- 



The Ordinates of Interest in Science at the American Asso- 

 ciation. 



The oscillations of interest in branches of science, and the rise 

 of, and rapidly increasing interest in, the more recent and some- 

 times the less difficult departments of learning, as well as the ap- 

 parent stagnation in the pursuit of science either locally developed 

 or affecting larger areas of population, have been often remarked. 

 It might seem reasonable to suppose that we might be able to re- 

 view with approximate accuracy the ebb and flow of the scientific 

 tide by watching the fluctuations of study in a representative and 

 national body of scientific workers ; in such assemblages as the 

 American, French, and English Associations present us with, where 

 no discriminations are made, and students of all grades and in- 

 clinations are welcomed. 



The obvious and feasible method to adopt for this purpose would 

 be to note the var}fing number of papers by different authors in the 

 several classes of study, and compare their aggregates distributed 

 over a number of years. This method we have used here, and yet 

 a little reflection will show that it is deceptive, and possibly in in- 

 stances leading to quite wrong conclusions. In the first place, 

 while the names of all scientific men in these countries, as a rule, 

 are found on the rolls of these associations, they may, for reasons 

 of convenience or personal comfort, or because they are asso- 

 ciates of smaller and more technically limited bodies, choose to 

 publish or read their papers elsewhere. In the second place, 

 many conscientious workers cannot enjoy the opportunity of at- 

 tending the meetings of the association, and, while authors in a 

 modest way, would be deterred from appearing upon so promi- 

 nent a platform, though they become members of the associa- 

 tion for the sake of enjoying its publications and the pleasure of its 

 recognition. Again, the ' ambulatory ' habits of the association 

 may carry it this year into a hot-bed of geologists or in their neigh- 

 borhood, and in another move it to the hunting-grounds of archse- 

 ology ; so that the method is defective as permitting just infer- 

 ences as to the fashion or currents of scientific investigations in the 

 association itself, and more evidently as regards the wholesale as- 

 pect of national scientific industry. 



And yet, with all deductions made, there is a residuum of interest 

 in the results of this examination. They show how evenly in some 

 branches the ' show of hands ' at the annual meetings of the asso- 

 ciation has been kept up, in others how the interest has fallen under 

 the entire average for years, and again risen by a recuperative effort 

 much above it ; they give an idea, at least, how some lines of study ^ 

 exceed others in their active participants in the association, an3' a« ' 

 measure of the rising importance or popularity of others. ' 



In computing the charts, the whole number of papers by differ- 

 ent authors in each department has been taken, and their percent- 

 age of all the papers read or accepted, by different authors, used to 

 fix the point of interest in the column corresponding to the number 

 of the meeting quoted. Where an author has prepared a paper on 

 two or more subjects, he is regarded as representing a unit of inter- 

 est in each ; but where he has offered a number on one subject, his 

 activity entitles him to no further recognition, for our purpose, than 

 the single contributions of others. The points of interest are meas- 

 ured from the base-line, and are meant to be strictly comparable ; 

 so that the greater general height of one series exhibits the pre- 

 ponderating value of that study. The determination of the proper 

 reference of a paper is in some cases not easy, and the lines might 

 in many ways be changed by a redistribution of the papers, ac- 

 cording as the statistician thought the contents of a paper shifted it 

 to a different though allied topic. 



Of course, the actual number of papers by different authors in 

 one subject may remain constant, while the percentage of interest 

 would show a decrease, from the re-enforcement of other depart- 

 ments and the consequent larger aggregate of individual papers 

 upon which to reckon. The most instructive conclusions, it seems 

 to us, are drawn from the relative position of the a^-erage line of 

 interest, in the different subjects, to the maxima and minima points 



