46 Prof. Bischof o?i the Natural History of 



AB represents the boundary between the solid crust of the 

 earth and the melted matters in the interior of the earth ; CD 

 represents a wide rent, exhibiting a communication from the 

 surface to the melted matters ; EF, GH, IK, LM, &c. are 

 narrow rents conducting water from the sea or subterranean 



o 



collection of water to the heated interior ;* and F, H, K, M 

 may be caverns in the solid crust, formed during the consoli- 

 dation of the originally fluid matters of a former period. Un- 

 der these circumstances it may easily be conceived, that water 

 penetrating into the above mentioned rents and caverns is con- 

 verted into steam, which, by pressing on the melted matters, 

 causes them to rise through the rent CD. If the lower opening 

 in the wide rent at D be on the same level as the whole bound- 

 ary between the solid rocks and the melted matters, small 

 quantities of these only will be raised upwards, for the surface 

 of the melted matters will soon sink below the opening of the 

 rent at 1), and steam will rise. Thus the elevation of a column 

 of lava to a considerable height by a column of steam will take 

 place. But if the lower opening of the rent CD descends more 

 or less below the surface of the melted matters, considerable 

 quantities of these will rise into it before this surface sinks be- 

 low the opening. The same may take place if between the 

 opening of the rent CD and the other rents (those down which 

 water flows from the surface), ridges of solid rock reach down- 

 wards from the solid crust into the fluid mass. 



Such ridges may be viewed as occasioned by gradual solidi- 

 fication of the fluid mass from above downwards, for it is well 

 known that melted matters, if they crystallise by cooling, exhi- 

 bit on their under surface considerable inequalities ; and the 

 consolidation of the melted matters in the interior of the earth 

 is assuredly produced by crystallisation. 



There is another circumstance which may cause a continuation 

 of the rent CD into the melted matters. After the rising of 

 the lava and steam in this rent, the walls of it are cooled by 

 the formation of steam, and by the atmospheric air having a 

 ready access to the empty channel. Therefore these walls 



* Water will naturally also penetrate into the wide rent, but, inasmuch 

 as it is not able to fill up the rent; it cannot confine the steam generated be- 

 neath, and the latter will therefore escape. 



