7 66 



THE POPULAR SCIENCE MONTHLY. 



for we have the authority of Prof. Law, cor- 

 roborated by the observations of Dr. Wood- 

 ward, for the statement that no "specific 

 vegetal germs have been found in the air, 

 blood, 05 nasal discharges, during the prev- 

 alence of the influenza." 



Elevation and Subsidence of the Earth's 

 Surface. The Philosophical Magazine for 

 December, 1872, contains an interesting pa- 

 per by Captain F. W. Hutton, F. G. S., " On 

 the Phenomena of Elevation and Subsi- 

 dence of the Surface of the Earth," from 

 which we condense the following : Assum- 

 ing the increase of heat of the earth's in- 

 terior to be 1 Fahr. to every 50 feet of 

 descent, there occurs at a depth of about 

 23 miles an. isogeothermal line or surface 

 where cohesion of the rocks is overcome 

 by heat, or rather would be so overcome at 

 the ordinary atmospheric pressure. But 

 the expansive force of the heat is balanced 

 by the pressure of 23 miles of superincum- 

 bent rock, and thus a general equilibrium 

 is maintained. The position of the earth's 

 surface is due to three causes : 1. Its own 

 weight ; 2. Support of the interior mass ; 

 and, 3. Lateral thrust of the various por- 

 tions against one another. 



Whatever disturbs this adjustment must 

 produce change of surface. If any eleva- 

 tion takes place in one section, there must 

 follow subsidence in another. A great de- 

 crease of pressure is, doubtless, brought 

 about by the radiation of heat into space, 

 but this the author insists does not account 

 for all the phenomena. There are two and 

 only two agencies constantly at work, ade- 

 quate to the production of this rise and fall 

 of surface, and these are denudation and 

 deposition, the latter being of greatest im- 

 portance. The isogeothermal line will con- 

 form itself to undulations of the surface ; 

 so that, if a deposition of 100 feet of sand 

 or rock occur, the line of heat will rise 100 

 feet, and the heat of the former line will 

 correspondingly increase. Citing experi- 

 ments of Colonel Totten and Mr. Adie illus- 

 trating the expansion of rocks by heat, the 

 author says : " If the overlying mass be of 

 loose particles, or sand, there could only be 

 such elevation as would arise from increase 

 of volume ; but in case of solid rock, as 

 limestone, there would be not only the in- 



crease of volume, but an arch-like elevation 

 arising from lateral thrust. From this 

 cause would arise ridges of elevation." 



In illustration of this, he refers to "the 

 well-known elevation of the Wealden and 

 Chalk of England. Here, with a thickness 

 of the Cretaceous of 2,100 feet and of the 

 Wealden of 1,300 feet, making in all 3,400 

 feet, we have a total rise of the arch of 

 about 4,100 feet, the total breadth being 

 about 100 miles. The elevation of the 

 nummulitic limestone of the Eocene is 

 also cited. This formation, 8,000 feet thick, 

 is an ocean-deposit extending from Spain 

 and Morocco to China and India, and has 

 been elevated into enormous ridges, as the 

 Atlas, Pyrenees, Apennines, and Himalayas. 

 The author suggests that the cooling of 

 mountain elevations as they rise above the 

 snow-line may reduce the temperature of 

 the surface, so that the rise of the isogeo- 

 thermal is arrested, and further elevation 

 ceases. On this point tables are given, 

 showing the rise due to certain depths and 

 areas of deposit. 



Denudation, like cooling of surface, is 

 supposed to induce subsidence in a given 

 area by causing the line of heat to recede. 

 But what could have disturbed the original 

 equilibrium ? " There can, I think, be but 

 one answer to this question, viz., the origin 

 of life on the globe. This life, by abstract- 

 ing the carbonate of lime from solution in 

 the sea, and depositing it on the bottom, 

 first disturbed the equilibrium." The writer 

 quotes freely from the statements of Bab- 

 bage, Herschel, Croll, Hopkins, and others, 

 to fortify points of this ingenious but per- 

 haps in some respects fanciful hypothesis. 



A Poison-Proof Bird. A correspondent 

 of Science Gossip tells of an attempt to 

 capture a specimen of the scavenger-bird, 

 or "adjutant," of India, in which he failed 

 in a most unexpected way. On account of 

 its valuable services in clearing the streets 

 of decaying and putrid matter, the bird is 

 held in high esteem by the natives, who 

 take every precaution to protect it from 

 harm. This prevented an open attack, and 

 poison was the only alternative. The car- 

 cass of a partially-dissected bat was stuffed 

 with enough arsenical paste and corrosive 

 sublimate to kill twenty men, and the titbit 



