222 GEOLOGICAL FACTS OBSERVED - '^ 



It has been observed to me, that what has been remarked on 

 the upper surfaces of the beds of Faroe, cannot be reconciled 

 with the ideas I had formed respecting the manner in which 

 the slagginess of the Mrtrfer surfaces had been produced. Though ^ 4 

 all I wish to contend for, in either case, is, that heat had ope- 

 rated, I request the indulgence of the Society, while I shortly 

 endeavour to show, how a lava, flowing at the bottom of the 

 sea, might also assume the marks of fusion on the upper sur- 

 face. 



The eflPect of water on the surface of metals in a state of 

 fusion, is well known to be the production of wrinkles. This 

 is the case also when any viscid substance, whether fluid by fu- 

 sion or otherwise, becomes gradually solid while in motion. 

 In the case of water applied to the surface of a hot body, the 

 phenomena are familiar to most persons. Wlien, for instance, 

 brass is in fusion, a few drops of water poured upon it remain 

 suspended almost without motion ; but as the heat dimini- 

 shes the water approaches nearer and nearer to the hot 

 surface, and at length coming into contact with it, violent 

 ebullition and quick evaporation take place. In the case 

 of a lava erupted at the bottom of a great depth of sea, a 

 stratum of steam must be produced, continuing, while the heat 

 exceeds a certain degree, to keep the water and the hot mass 

 separate. In the operation of boiling the mercury in a baro- 

 meter tube, an event analogous to this takes place, and we see 

 the column of mercury raised up by the vapour occupying the 

 lower end. As the heat of a stream of lava flowing under the 

 sea is reduced, and the lava itself becomes viscid, its mo- 

 tion, combined with the action of the water coming into 

 contact with it, will infallibly produce a surface full of 

 wrinkles ; and therefore we should expect to find the upper 



surfaces 



