January 22, 1886.] 



SCIENCE. 



79 



River' slates in Orange county, N.Y., arid else- 

 where." 1 



In this paper I described the finding of Trenton 

 fossils in slates that Emmons had always considered 

 to be of Taconic age ; and Professor Mather's 2 state- 

 ment that the remains of 4 Testacea ' were found at 

 certain localities in these states appears to have been 

 overlooked in Emmons's latest discussion of the sub- 

 ject (likewise in that of Dr. Hunt' 1 ). In calling 

 attention to the nature of these remains, and adding 

 a new locality, with descriptions of the structure of 

 the beds, I was only presenting bare statements of 

 facts ; but, in consideration of the Taconic theory, I 

 employed the words * Fossils in the Hudson Eiver 

 slates,' etc., rather than ' Trenton fossils in the 

 Taconian argilhte.' in my title. 



It can be readily understood how isolated patches 

 of Utica slates could extend along the Hudson valley 

 as far south as noted by Booth ; 4 but my observations, 

 together with those of Dale, 5 show the occurrence of 

 Trenton fossils in beds at several widely separated 

 points in the slate belt (I have discovered other 

 localities since my paper), and point to the age of the 

 great mass of these slates as post-Potsdam. An 

 examination of the relations at Rock Tavern and at 

 Sugar Loaf plainly proves that the fossiliferous beds 

 are not isolated patches, and that neither are they 

 superficial layers enclosed in synclinal folds, nor 

 brought to their present positions by faulting. 



In this connection it may be well to state that for 

 some time the writer has been engaged upon a very 

 detailed study of the structure of these slates, and 

 the associated limestones and other formations. 

 Many paleontological and stratigraphical discoveries 

 have been made which will solve some of the prob- 

 lems of their ages and relations. A portion of the 

 results of this work will be ready for publication 

 early in the next summer. 



Nelson H. Darton. 



Brooklyn, N.Y. 



The temperature of the moon. 



I hope that Professor Ferrel and I have no real 

 ground of dispute : I may at least think so, since he 

 does not deny that he begins by speaking of a certain 

 body endowed by hypothesis with peculiar properties ; 

 such, for instance, as imply invisibility. Professor 

 Ferrel, as I now understand him, explains that this 

 implication is non-essential, and merely an analytical 

 device to explain what would take place on a certain 

 sphere, on which (by hypothesis still) the relative 

 radiating and absorbing powers of every part are 

 not merely proportional for any given ray, but to 

 be safely treated as absolutely and without restric- 

 tion equal, — a sphere on which, instead of physical 

 approximations, we have absolute truths, which, like 

 the axioms of Euclid, can be safely pushed to their 

 extremest consequences. 



This sphere it is my complaint that Professor 

 Ferrel identifies with the moon, though it also seems 

 to be a homogeneous body, not a world of irregular 

 surface and structure ; a body freed from changes of 

 temperature, and which (unless infinitely conduct- 

 ible) would appear to need, not to alter its distance 

 from the sun or rotate on its axis, — an absolutely 



1 Amer.journ. sc. (3d ser.), xxx. p. 452, 1885. 



2 Final report, 1843, p. 369. 



3 The Taconic question, Trans. Roy. soc. Canada, vol. i. 



4 Amer.journ. sc. (3d ser.), xxvi. p. 380, 1883. 



5 Ibid., xvii. p. 57, 1879. 



airless body ; and so on, through a really endless list 

 of limitations, which we should find, on scrutiny, la- 

 tent in his premises. Under these limitations, I do not 

 dispute any of his conclusions ; nor, when I say that 

 no actual body in nature does exist under them, 

 do I at all deny his right to consider one which 

 by hypothesis shall do so, nor the interest of such 

 an inquiry. I only call the reader's attention to 

 the undoubted fact that the real moon exists 

 under quite other ones. While I do not for a 

 moment admit that the temperature of the real 

 moon is independent of the amount of heat which 

 it rejects by reflection, I can readily agree that 

 it might be quite immaterial to the temperature 

 of this hypothetical moon. I have no disposition 

 to treat such an hypothesis as idle : I acknowledge 

 its interest, and, I may add, its utility, if employed 

 under clearly recognized limitations. 



I recognize with respect the accuracy of the logical 

 process always at Professor Ferrel's command ; but, 

 I repeat, the more accurate it is, the more certain it 

 is to deduce only such conclusions as are implicitly 

 contained in its premises. 



Though he himself refers in part to these limita- 

 tions at the outset, the general reader may certainly 

 require to be reminded that they are not embraced 

 in Professor Ferrel's conclusions, which may well be 

 deduced from commonly made assumptions, by cor- 

 rect reasoning, as to a hypothetical moon, and yet 

 not apply without limitation to the real one which 

 we see waxing and waning in the sky. This is all I 

 have to say, and I leave to Professor Ferrel the last 

 word in this friendly controversy if he chooses to 

 add it. S. P. Langley. 



Allegheny observatory, Jan. 12. 



Demand for good maps. 



I am very glad that you have taken upon yourself 

 to criticise our maps and the map-makers' methods, 

 and sincerely hope that you may succeed in so stir- 

 ring up the publishers that they will feel compelled to 

 abandon the habit of servilely copying ancient, and 

 ofttimes obsolete examples. I have been seriously 

 inconvenienced at times, particularly when giving 

 instruction in geography, by the outrageous careless- 

 ness, not to say gross ignorance, displayed by our 

 leading cartographical institutions. 



I heartily concur in what Mr. C. H. Leetesays con- 

 cerning the German maps. We are far indeed from 

 their standard. Why is it ? It is no exaggeration 

 to say that the cheap German school-atlas, to which 

 Mr. Leete refers, is much more reliable, and more 

 nearly up to date, even in the geography of the 

 United States of America, than the most expensive 

 of our home productions. 



Some years ago the travelling agent of one of our 

 leading map-publishing houses called upon me, and 

 insisted upon showing me their latest atlas, revised 

 and corrected to date. I gave him every opportunity 

 to explain the superior excellence of his wares, and, 

 after he had had bis say for over half an hour, I showed 

 him that most of his maps were exact copies of those 

 published from five to twenty-five years previously, 

 the only apparent change being in the shades and 

 elaboration of colors. Why, actually, though this 

 was scarcely five years ago, the map of New York 

 city showed the ' Crystal Palace ' ! Even where de- 

 tails appeared to fill in former blanks, more than 

 one-third were mere guesses, and about as good 



