THE ORIGIN OF LUNAR VOLCANOES. 51 



I have watched the cooling of such masses very fre- 

 quently, and have seen abundant displays of miniature 

 volcanic phenomena, especially marked where the cooling 

 has occurred under conditions most nearly resembling those 

 of a gradually cooling planet or satellite; that is, when the 

 fused cinder has been enclosed by a solid resisting and con- 

 tracting crust. 



The most remarkable that I have seen are those pre- 

 sented by the cooling of the "tap cinder" from puddling 

 furnaces. This, as it flows from the furnace, is received in 

 stout iron boxes ("cinder-bogies") of circular or rectangular 

 horizontal section. The following phenomena are usually 

 observable on the cooling of the fused cinder in a circular 

 bogie. 



First a thin solid crust forms on the red-hot surface. 

 This speedily cools sufficiently to blacken. If pierced by a 

 slight thrust from an iron rod, the red-hot matter within is 

 seen to be in a state of seething activity, and a considerable 

 quantity exudes from the opening. If a bogie filled with 

 fused cinder is left undisturbed, a veritable spontaneous 

 volcanic eruption takes place through some portion, gener- 

 ally near the centre, of the solid crust. In some cases, 

 this eruption is sufficiently violent to eject small spurts 

 of molten cinder to a height equal to four or five diame- 

 ters of the whole mass. 



The crust once broken, a regular crater is rapidly formed, 

 and miniature streams of lava continue to pour from it; 

 sometimes slowly and regularly, occasionally with jerks 

 and spurts due to the bursting of bubbles of gas. The ac- 

 cumulation of these lava-streams forms a regular cone, the 

 height of which goes on increasing. I have seen a bogie 

 about 10 or 12 inches in diameter, and 9 or 10 inches deep, 

 thus surmounted by a cone above 5 inches high, with a base 

 equal to the whole diameter of the bogie. These cones and 

 craters could be but little improved by a modeler desiring 

 to represent a typical volcano in miniature. 



Similar craters and cones are formed on the surface of 

 cinder which is not confined by the sides of the bogie. I 

 have seen them well displayed on the "running-out beds" of 

 refinery furnaces. These, when filled, form a small lake 



