August 10, 1906.] 



SCIENCE. 



165 



tion lias played in giving configuration to 

 its surface, and the absence of any in- 

 fluences which would alter the aspect or 

 general make-up of the surface outside of 

 volcanic disturbances. The markings 

 alluded to as existing around such craters 

 as Tycho and Copernicus, as well as the 

 great depth and other marked character- 

 istics of these and similar craters, declare 

 them to be the more recent of the great 

 volcanic outbursts on the lunar surface. 

 They bear the impress of having been very 

 violent, and -the vapors indicate ejections 

 hot up to the point of vaporization. If 

 the view presented is correct, this is entirely 

 natural^ On the other hand, contrast these 

 craters with those called Archimedes and 

 Plato, lava plains, surrounding which we 

 see no vapor or fume streaks, and no evi- 

 dence of great violence, and we are brought 

 to infer that these latter are the results of 

 more ancient action in the nature of more 

 gentle welling up from below of fused mat- 

 ter, not so greatly heated by the energy of 

 expulsion. Such craters are shallow and 

 were probably more in the nature of quies- 

 cent pools or lakes of lava than great relief 

 vents from great depths traversed by ma- 

 terials at high velocity and at the high 

 temperatures brought about by the process 

 of superheating while moving against re- 

 sistance in volcanic pipes. So far then as 

 the moon furnishes evidence on this sub- 

 ject it may well repay further study, and 

 its condition seems to confirm the position 

 taken herein. It has sometimes been 

 claimed that much of the explosive effect of 

 gas and steam from volcanoes may be due 

 to water entering or percolating through 

 heated strata and being converted into 

 steam at enormous pressures. But the pos- 

 sibility of this is doubted. The very pres- 

 sure of vapor would stop the process at its 

 outset. No water would enter a hot stratum 

 unless forced in by a pressure in excess of 



that which the steam would acquire upon 

 its generation. A boiler can not be fed with 

 water by a pump which yields less pressure 

 than that carried by the boiler itself. 



If, however, the water be already present 

 in a rock stratum which is invaded by hot 

 lava rising in a volcanic fissure, then its 

 conversion into steam and the violent emis- 

 sion thereof may readily take place. 



It is conceivable too that considerable 

 movement or shifting under pressure of any 

 moist stratum over considerable distances, 

 especially through a restricted channel, 

 may result in heating it to a temperature 

 sufficient to generate steam. Here again, 

 as in the case of the rock flow before re- 

 ferred to, the work done in moving the 

 particles against great resistance may un- 

 der proper conditions cause an accumula- 

 tion of heat energy sufficient to account for 

 explosive effects when the material reaches 

 a vent. Under such conditions also, the 

 expulsion of hot mud or sand with steam 

 may occur without the concurrence of lava 

 flow. 



The considerations herein put forward 

 seem to furnish a basis for a dynamical 

 theory of volcanoes. Doubtless the action 

 of heating a flowing rock by energy ex- 

 pended upon it may be, and perhaps is, 

 often supplemented by other causes, such 

 as chemical action brought about by hot 

 contact of substances having affinity for 

 each other. Gaseous products under high 

 pressures may be the consequence of the 

 reactions. Limestone or other carbonate 

 may be decomposed by the contact of hot 

 lava, and carbonic acid gas in great vol- 

 umes be thus liberated. 



We certainly have no need of recourse 

 to an assumption of the existence of large 

 localized bodies and radium minerals to 

 explain volcanic action. To say the least 

 such an assumed store of this rare element 

 is improbable. 



