140 GEOLOGY OF THE HIGH PLATEAUS. 



as they are useful or otherwise in explaining a wider and wider range of 

 facts. This was true of the hypothesis of a luminiferous ether and of 

 gravitation. Neither of these postulates could be proven a priori, and have 

 gained acceptance because they explain all facts to which they stand re- 

 lated. Following these precedents, we may inquire whether a rise of sub- 

 teiTanean temperature is consistent with other categories of facts besides a 

 succession in the order of eruptions and explains other phenomena. 



I have endeavored to show that the whole tenor and purport of the phe- 

 nomena of volcanicity point to the conclusion that lavas are not primordial 

 liquids but secondary products derived from the liquefaction of solid matter 

 situated below the surface in layers or maculae. Of this statement of the case 

 in its grosser aspect I believe the circumstaiitial evidence sufficient to con- 

 vince a scientific and impartial jury. Taking a generalized view of the sub- 

 ject, the objections against primordial liquids are insuperable. If the whole 

 interior of the earth below a crust a few miles in thickness is liquid, the sta- 

 bility of that crust is intelligible only on the assumption that the crust is less 

 dense than the liquid, and if the reverse is true it seems inevitable that the 

 crust would be speedily submerged. The same reasoning would be appli- 

 cable to residuary vesicles or primordial reservoirs of great extent under- 

 lying states and empires. If we adopt the conception of a multitude of 

 small vesicles left by the secular consolidation of the globe gradually 

 squeezed out one after another, other difficulties equally palpable arise. 

 These vesicles should, in the process of ages, become fewer and fewer, and 

 show signs of exhaustion. But observation teaclies us that the eruptions of 

 Tertiary time are apparently as numerous, as varied, and as grand as any 

 which have occurred in anterior ages. But, above all, the intermittent 

 pulsating character of the eruptions in any volcanic cycle is at variance 

 with such an assumption. If this primordial liquid has lain in its receptacle, 

 possessing, from the beginning of the world, all the essential requisites of 

 eruptibility except that it is waiting for some accident to open a vent for 

 it, yet, when the vent is once opened, why does it not pour forth at one 

 mighty belch all its lavas and then close up forever? Why should it re- 

 quire some hundreds or even thousands of eructations with intervals of 

 years to completely exhaust it? Wliy, in the course of the cycle covering 



