272 SEE— TEMPERATURE, SECULAR COOLING [April 20, 



and then returns after the currents have met and raised a ridge 

 in the centre of the depression. By no possibiUty can we interpret 

 Aristotle's account to indicate an elevation of the sea bottom, as 

 when a volcano is upheaved, which would cause the waters to rise 

 suddenly without previous recession from the shore. The only 

 other class of sea waves is that in which the water retires after the 

 earthquake, and Aristotle's language distinctly implies that this re- 

 cession took place. Moreover, Strabo says that the disaster was 

 attributed to the anger of Poseidon, '' the earth-shaker," to whom 

 were ascribed the sea waves accompanying great earthquakes. 



If this view be admissible, it will follow that the sinking of 

 Helike was by the usual process of subsidence in seismic sea waves 

 of the first class, except that the subsidence of the bottom of the 

 gulf carried down also part of the shore. As the gulf is quite 

 narrow such a result is probable in the highest degree. 



This sinking of the shore along the bed of the sea is not 

 unusual even where the sea is wide; but for the sake of conven- 

 ience of diction we have ordinarily spoken only of the sinking of 

 the sea bottom rather than of the land along the shore. Unless 

 there is movement of a fault with vertical walls, the change of level 

 is naturally gradual, depending on the yielding and flexure of the 

 earth's crust when lava is injected or expelled from beneath it. 

 § 24. Further Considerations on the Elevation of the Himalayas, 



Based on the Relief of the Indian Ocean at its Margins. 



In the paper on the cause of earthquakes we have explained the 

 Himalayas by the expulsion of lava from beneath the Indian Ocean, 

 and have attributed the continuance of earthquakes in that region 

 to the activity of the ancient sea trough where the Ganges and 

 Bramaputra now flow. The process there is similar to that found 

 in the Andes, but the mountains are now somewhat further from 

 the sea. In calling attention to the surface leakage in the region 

 south of the Himalayas, there was no thought of implying that the 

 effect of the ocean has ceased; on the contrary there can be no 

 doubt that strain beneath the Indian Ocean's crust is still relieved 

 by the same movements which originally formed and are still rais- 

 ing the Himalaya mountains. The surface waters augment the 

 effects of the relief of strain from beneath the sea, and these two 



