388 



CRATEES AND STRIAE. 



CIIAPTE 

 X-WIII 



Exi.l:in:iti 

 of pheno- 

 aiena. 



Trnchylic 

 domca. 



Anoieist 



R the cause of the multitude as well as of the mau;nitu(le of 

 these volcanoes. As tlie outer crust cooleJ, tlie moon 



n would become, so to speak, hide-bound, and, by the con- 

 traction of the surface upon the liquid mass beneath, the 

 latter would be spurted out in every direction, while the 

 foi'mer would also exliibit those radiating striae or cracks 

 which are so very marked a feature in its appearance. 

 Some of these cracks are upwards of 700 miles long. In il- 

 lustration of the mode in which it is probable this appear- 

 ance was produced in the moon, Mr. Naysniith showed 

 portions of glass globes, which, after being filled with hot 

 water, and then hermetically sealed, were broken by the 

 application of cold to the outside. Besides the craters 

 and tliese striae, there are also many trachytic domes, 

 where the force of ejtction has not been sufficiently great 

 to form craters ; and lastly, there are great ranges of hills, 

 the formation of which appears to have taken place in 

 this way : — as contraction goes on, the liquid nucleus 

 separates itself from the solid crust ; the latter is bent 

 inwai-ds by the force of gravitation, and a cracking and 

 crushing action takes place, with farther eruptions in 

 mountain crests ; or two adjacent surfaces are raised edge 

 on edge as in fields of ice. A shrivelled apple maj' be 

 referred to as affording a familiar illustration of this ap- 

 peai'ance and its cause. 



Several volcanoes are described by ancient Chinese 

 writers, wlio also mention a variety of volcanic products, 

 sucli as sal ammoniac and sulphur, which form articles 

 of commerce. " We thus know," says Humboldt, " in 

 the interior of Asia, a volcanic territorj-, the surface of 

 which is u])\vards of 2500 square geographical miles, 

 and wliicli is from 1400 to 1800 miles distant from the 

 sea. It fills the half of the longitudinal valley situated 

 between the first and second system of mountains. The 

 jirincipal seat of volcanic action appears to be in the 

 Thian Chan. Perhaps the colossal Bokhda-oola is a 

 trachytic formation like Chimborazo." On both sides of 

 the Thian Chan violent earthquakes occur. The city of 



