THE CRUST AND INTEEIOR OF THE EARTH. 217 



This doctrine lias for a long time been accepted by geologists as a 

 fundamental principle of their science. Their researches not only 

 corroborate this theory, but supply evidence which, coupled with the 

 results of observation as to movements now going on in the earth's crust, 

 shows that the process of cooling and consolidation is still in operation. 



The phenomena of volcanoes would appear to afford direct evidence 

 of the interior of the earth being still in a state of intense heat. In a 

 paper submitted to the Eoyal Society in 1874, Mr. Robt. Mallet 

 attributed the heat by which volcanic eruptions are pi-oduced to the 

 effect of friction resulting from the crushing of solid rocks in the cooled 

 surface. This view had not met with much acceptance ; but, as Mr. 

 Mallet accounted for the crushing of the crust by the contraction of the 

 interior in the process of cooling, his theory was not inconsistent with 

 the general theory of a cooling earth. 



The undulatory movement of the earth's crust, shown by the 

 elevation and depression of the surface, is conclusive evidence that the 

 interior of the earth is not solid. There is abundant evidence of 

 such movements in former geological periods, and at the present 

 time. In the Malvern area a gi-eat part of the older rocks have 

 sunk, and new red deposits have taken their ^place. At Svvdndon, 

 in Wiltshire, the quarries disclose the remains of an old land 

 surface, which first sunk and became covered with deposits of 

 the cretaceous sea, and was then re-elevated for the enjoyment of 

 terrestrial beings. The Suffolk coast shows similar movements in recent 

 geological times. Sir 0. Lyell, Professor Ramsay, and other authorities 

 testify to similar movements in recent times in Africa, South America, 

 Northern Asia, British Columbia, and the Pacific, and particularly to 

 the elevation of Sweden and the Baltic, now progressing at the rate of 

 2J feet in a century. 



At a recent meeting of the Geological Society, Captain Fielden, the 

 Natui'alist to the recent English North Polar Expedition, stated that at 

 the present time the coasts of Greenland and Grinnell Land are steadily 

 rising from the sea. These movements prove conclusively that the 

 earth is not yet sohd. They would be explained, if the earth con- 

 sisted of a mass of mixed substances, such as we are acquainted with 

 as forming its crust, still for the most part in that viscid or 

 yielding condition, which we know that they assume when passing from 

 the molten to the solid state in cooling, such for instance as lava, 

 glass, iron, basalt, &c. 



Can the earth's pristine heat be still retained in it ? Assuming 

 that it was once heated, its heat could only escape tlu-oiagh the 

 crust. If the crust consisted of absolutely non-conductive materials 

 it would never lose its heat. The crust is not of such a character, but 

 the materials which form its bulk are slow conductors. The escape of 

 heat would become slower as the crust thickened. 



Observations of underground temperature show that the heat 

 increases at the rate of one degree Fah. for every 60 feet. This gives a 

 temperature of 2,500 F. at about thirty miles from the surface. At such 

 a temperature lava would be as liquid as water. Pressure may condense 



