270 On the Structure of the Lunar Surface. 



the most earnest and careful attention of geologists, as the 

 most probable and satisfactory explanation of the cause of 

 those vast torrents, of which the boulder and gravel covered 

 surface of extensive districts of the earth yield the most 

 striking evidence. Thus we have then, in this grand but 

 simple action of the progressive collapse of the crust of the 

 earth following down after the retreat of the contracting in- 

 terior, the cause of those tremendous earthquakes, the evidence 

 of which is so clearly indicated by faults and dislocated strata. 

 The origin or cause of those bright lines which radiate 

 from certain volcanic centres on the moon's surface (Tycho, 

 for instance) is alluded to, and illustrated by a very striking 

 experiment of causing the surface of a globe of glass filled 

 with water to collapse on the fluid interior by rapidly con- 

 tracting the surface while the water has no means of escape. 

 The result was the splitting or cracking up of the surface of 

 the globe in a multitude of radiating cracks, which bear the 

 most remarkable similarity to those on the moon. Mr 

 Nasmyth further illustrated this subject by reference to the 

 manner in which the surface of a frozen pond may be made 

 to crack by pressure from beneath, so yielding radiating 

 cracks from the centre of divergence where the chief dis- 

 charge of water will take place, while simultaneously all 

 along the lines of radiating cracks the water will make its 

 appearance ; thus explaining how it is that the molten mate- 

 rial, which had in like manner been under the surface of the 

 moon during that period of its history, came forth simulta- 

 neously up through the cracks, and appeared on the surface 

 as basaltic or igneous overflow, irrespective of surface inequa- 

 lities. Mr Nasmyth concluded his address by an earnest 

 appeal to his geological hearers to test the correctness of what 

 he had advanced, by a careful inspection of those vast natural 

 records of the changes which the earth's surface has under- 

 gone, of which our mountains, hills, and valleys, are the 

 mighty monuments, and which shadow forth, in characters 

 which science can trace, past events of the most surpassing 

 interest and grandeur, inasmuch as they are the evidences of 

 the handiwork of the all-wise Creator, when preparing the 

 earth for the advent of man. 



