Lunar Surface, and its relation to that of the Earth. 269 



much less on the surface of the moon than on the earth, so 

 that the collapse action had to operate on material probably 

 not half the weight of cork, bulk for bulk. 



The causes of those vast ranges of mountains seen on the 

 moon's surface were next touched on ; and Mr Nasmyth endea- 

 voured to explain them by the continued progress of the col- 

 lapse action of the solid crust of the moon crushing down or 

 following the contracting molten interior, which, by the 

 gradual dispersion of its heat would retreat from contact 

 with the interior of the solid crust, and permit that to crush 

 down and so to force that portion of the original surface out 

 of the way, and in consequence of this action assume the form 

 and arrangement of mountain ranges. Mr Nasmyth, in illus- 

 tration of this important action, adduced the familiar case of 

 the wrinkling of the surface of an apple, by reason of the 

 contraction of the interior, and the inability of the surface to 

 accommodate itself to the change otherwise. The mountain 

 ranges in question Mr Nasmyth considers to be nothing 

 more or less than the material which in the original expanded 

 globe foi*med the comparatively level crust of the moon. 



The fall of the unsupported crust on the retreating nucleus 

 was described to yield a very probable explanation of the 

 appearance of granitic and igneous centres of certain moun- 

 tain ranges, as well as the injection of igneous rocks in the 

 form of trap dykes and basaltic formations, which appear to 

 have come forth in this manner from below the crust of the 

 earth, and to have overlaid formations of comparatively very 

 recent formation. 



The partial and gradual retreat of the molten interior or 

 nucleus from the solidified crust was in like manner sug- 

 gested as the most probable cause of the submersion of large 

 portions of what had previously been dry land, causing, when 

 on a comparatively small scale, " basin formations," and when 

 on a vast scale,' and with more sudden action, occasioning the 

 influx of the ocean over the submerged continent, the waters 

 hurling along with them fragments of rock, denuding the sur- 

 face of the submerged land, and scattering its surface with 

 the wreck in the form of boulders, gravel, sand, and clay. 



Mr Nasmyth suggests the above contracting theory to 



