192 



SCIENCE. 



[Vol. I., No. 7. 



higher on the west side of the break than on the east 

 side, and duplicated by the lateral and upward thrust 

 for nearly two feet before it droops to and passes into 

 the smutty coal of the break. 



From what is exposed, it appears that a part of the 

 upper hill, at least down to and including the coal 

 and fire-clay, has, from some cause, moved on the 

 underlying strata; and at the fault the coal-bed has 

 been broken and forced upon itself for two or three 

 feet. The coal next the mouth not partaking of the 

 motion of that farther in the hill, I could find no 

 detritus of the removed part of the top coal, 10 to 18 

 Inches of which is wanting from the opening to the 

 fault. This would tend to prove that the faulting 

 might have occurred in carboniferous times. The 

 exposure of the roof-shales is not suflicient to prove 

 the absence of such detritus. The condition of the 

 coal at the line of fault would point to a geologically 

 recent date of disturbance. Jefferson county is out- 

 side the region of glacial drift. Samuel Huston. 



Richmond, Ohio. 



The Leadville porphyry. 



In the American naturalist for November, 1882, I 

 find the following note : — 



" The so-called Leadville porphyry. —FmfeeBor Alexis Ju- 

 lieu read a paper at the Montreal meeting of the American asso- 

 ciation, on this subject, in which be described the result of bis 

 examination of the rock In question, in thin sections under the 

 microscope. He finds that it is not an eruptive rock, hut is sedi- 

 mentary. Its material consists of tlie ddbrif; of the erosion of 

 Plutonic rocks redeposited in the Silurian ocean. He concludes 

 that the rock is not a porphyry, but must be called a felsite tufa. 

 The importance of this conclusion in estimating the form of any 

 metallic ores contained in this deposit is obvious, and will be 

 invaluable to mining experts." 



Having spent the better part of two years in a de- 

 tailed study of the Leadville region, an abstract of 

 the results of which was published about a year since, 

 I feel it my duty to correct any misapprehension 

 which may arise from the above statement. The 

 paper to which it refers I have not yet been able to 

 see, and cannot, therefore, tell exactly to which of 

 the many varieties of porphyry occurring at Leadville 

 Professor Julien refers. I have seen slides of his in 

 the possession of a gentleman at Leadville, which I 

 have reason to believe were made from specimens of 

 the rocks to which I gave the local name of 'gray 

 porphyry,' and which had been labelled by him ' fel- 

 spathi'c gneiss.' To whatever porphyry he may refer, 

 however, I have no hesitation in saying, that his mi- 

 croscopical determinations have led him utterly astray. 

 On what ground he decides from the simple inspec- 

 tion of a thin section of a rock of this character, 

 whether it is sedimentary or eruptiye, I am unable to 

 conceive. Microscopical lithologists in Europe, and 

 their pupils in this country, hesitate to do this with- 

 out the aid of field-observation; and, as far as I know, 

 it is only a few Americans who have obtained their 

 knowledge of this science independently of such ad- 

 ventitious aid, — and who therefore, in their own 

 opinion, know much more than those who originated 

 the science, — that feel themselves competent to de- 

 cide on the character of a rock without any knowl- 

 edge of its field-habit or mode of occurrence. The 

 mischievousness of this assumption is illustrated in 

 the present case, where an utterly mistaken statement 

 is given to .the public by one whose name and position 

 should be guaranties of scientific accuracy. Quite 

 aside from any microscopical evidence, — as regards 

 which, it is unnecessary to say, I differ essentially 

 from the above-quoted statement, — all the Leadville 

 porphyries are most dlstinclly eruptive. They occur 

 largely as sheets between sedimentary beds, it is true; 

 but they also cross these beds, occur as dikes, and 



carry within their mass larger or smaller portions of 

 the enclosing sedimentary beds, as caught-up frag- 

 ments. 



To the writer of the above-quoted article, I would 

 say, that, though in one sense a mining expert myself, 

 I fail to see any possible use which Professor Julien's 

 conclusions, had they been correct, would have been 

 to me ' in estimating the form of any metallic ores 

 contained in this deposit,' even had the Leadville 

 ores been contained in porphyry, which, as a rule, 

 they are not. S. F. Emmons. 



U. S. geological survey, Washington, D.C. 



Sand-tracery. 



My attention was called last fall to the curious 

 markings, formed chiefly by the agency of plants and 

 wind, on the beach of Lake Champlain. Seeing a 

 notice of similar phenomena observed on the seashore 

 by a correspondent in the second number of Science, 

 I would add the following, which tends only to con- 

 firm some of his statements: — 



In passing over the smooth beach of Burlington 

 Bay, one is struck, first of all, by the porous condition 

 of the sands just outlying the portions within reach 

 of the waves. Unacquainted with this appearance, 

 he might attribute it to some sand-boring insect, did 

 not a closer observation teach him at once that it was 

 eifected by the spray, and due to the bursting of air- 

 bubbles. The sand sifts over these holes until they 

 are entirely concealed, or only a small opening is left, 

 out of which one might not be surprised to see an 

 insect emerge at any moment. He would also noticfe 

 numerous tracings referable to the tracks of small 

 animals. These are frequently regular and clean cut, 

 and resemble impressions which are seen in the tri- 

 assic sandstones of the Connecticut river. Again: a 

 little observation stands one in good stead, as it 

 shows these to be made by dry frizzled algae, rolled 

 onward by the wind, as was remarked in the letter 

 above referred to, or sticcessively raised and dropped, 

 making still more deceptive impressions. A leaf is 

 often trundled along by a slight breeze, indenting the 

 sand in a very regular, though seemingly fantastic 

 manner. 



Furthermore, I have frequently noticed a curious 

 print made by the pliant stem of an alga, which had 

 become attached at one end. The remaining por- 

 tions, being at the sport of the wind, describe concen- 

 tric circles" at every point of contact. I thought at 

 the time how little imagination would be required to 

 endow such simple examples of nature's geometry 

 with the higher characteristics of plants and animals. 

 Would it not be worth while for some one who has 

 the opportunity and leisure to make a comparative 

 study of these markings, and determine how many 

 of such trifling phenomena have been exalted higher 

 than they deserve ? F. H. Herbick. 



Burlington, Vt., liaroh ], 1883. 



WHITNEY'S CLIMATIC CHANGES.^ 

 IIL 



The second part of this article discussed the 

 relation of a general change of atmospheric 

 temperature to glaciation. We now come to 

 consider its relation to desiccation. 



Because all precipitation depends on evap- 

 oration, and because rate of evaporation di- 



1 Concluded from No. 6. 



