October 10, 1902.] 



SCIENCE. 



593 



THE LAWS OF PHYSICS. 



Professok C. E. Van Hise, in his excellent 

 address on the training and work of a geol- 

 ogist (Science, August 29), criticises the 

 spiritualistic views of Dr. A. R. Wallace (p. 

 333) on the ground that they show an igno- 

 rance of physical laws. If Professor Van Hise 

 were more familiar with Dr. Wallace's wri- 

 tings, he would know that that naturalist is no 

 mere biologist, but is well acquainted with 

 the currently accepted laws of physics. If he 

 should remain unconvinced of this, he could 

 not say that Professors Crookes and Oliver 

 Lodge, who hold similarly heterodox opinions, 

 are not familiar with the principles of physics ! 

 It seems to me that Professor Van Hise might 

 just as well have claimed that believers in 

 magnetism were unacquainted with the laws 

 of gravitation. 



Some years ago I had the pleasure of dis- 

 cussing these matters with Dr. Wallace, and 

 in my innocence I ventured to ask if he had 

 sufficiently considered the laws of physics, and 

 so forth. I can recall his smile as he said that 

 of course he had considered them, and then 

 went on to say that all phenomena were 

 equally natural and in accordance with natural 

 laws, only some had received a theoretical 

 explanation, while others had not. 



Dr. Wallace's views may or may not be 

 absurd, but it seems clear that Professor Van 

 Hise's criticism is without justice or validity. 



T. D. A. OOCKERELL. 

 September 12, 1902. 



LICHENS ON ROCKS. 



To THE Editor of Science : A few days 

 ago, I visited a point along Chicago Creek 

 near Idaho Springs, Colorado, and on ex- 

 amining the massive rock (gneiss) to ascer- 

 tain the cause of the apparent weathering, I 

 found the rocks literally covered with lichens 

 of a uniform black color. 



My observations were made in the vicinity 

 of an abandoned tunnel site, in fact at the en- 

 trance, and while standing on the ' dump ' my 

 eye fell upon a piece of porphyritic rock which 

 proved to be covered with arborescent figures 

 closely resembling the imprint made by the 

 lichens observed on the rocks above. 



My first impressions were that the figures 

 were simply those characteristic of ' dendrites,' 

 but on further examination and reflection I 

 discovered that the deposit on my specimen 

 was upon the surface of a conchoidal frac- 

 ture, the latter being evidently the result of 

 a shot made prior to the removal of the rock 

 from the fissure vein, and consequently the 

 arborescence could not be the result of the in- 

 filtration of a mineral solution along a cleav- 

 age plane or fissure, which is generally sup- 

 posed to be the cause of such deposits. 



This conclusion was seemingly corroborated 

 by a discovery made a few moments later on 

 the opposite side of the canon and at the 

 base of another mountain. Here I found a 

 magnificent hand specimen of porphyry 

 which was evidently derived from a porphyry 

 dyke which I know to be located several hun- 

 dred feet above the creek. The entire surface 

 of the specimen which had been exposed to the 

 light was covered with beautiful forms of li- 

 chens of a brown, green, gray and black color,, 

 brown and green predominating. 



The ground or main mass of the por]'hyry» 

 consisting of a beautiful brown color in which 

 were embedded the crystals of feldspar, led me 

 to think that perhaps the difPerentiation in 

 the color of the lichens was due to the mineral 

 content of the underlying constituents of the 

 rock; for the greater percentage of the browns 

 were found growing in the brown main mass. 

 Here was also evidenced their corrosive and 

 etching efPect upon the rock, the black li- 

 chens being evidently in a state of decomposi- 

 tion ; their corrosive and penetrating effect was 

 also quite apparent upon the massive rocks, 

 resulting in beautiful arborescence similar to 

 that found in the specimen first alluded to 

 above. 



I might add that the specimen was consid- 

 erably mineralized, iron pyrites being dissemi- 

 nated throughout and readily observed by the 

 naked eye. The presence of this accessory 

 together with that of the essential oligoclase 

 which might possibly contain manganese as 

 one of its constituents leads me to ask, first, 

 whether either one or both of these minerals 

 could have influenced the color of the plant 

 during life, second, whether the arborescence 



