On the Agency of Water in Volcanic Eruptions. 159 



2nd. The rate of increase of temperature with the increase of depth 

 from the surface. 



3rd. The volcanic phenomena of the present day, and the welling- 

 out of the vast sheets of trappean rocks during late geological 

 periods. 



a. It is important for our object to note that not only has moun- 

 tain-uplifting gone on through all geological time, but that many, if 

 not most, of the great mountain chains have been raised during the 

 latest geological periods, and that compressed uplifts have not been 

 confined to any limited district, but have extended over the several 

 continents and over both hemispheres. As instances of these may be 

 named : — 



1. The elevation of the Pyrenees, which, although commenced in 



Palaeozoic times, attained its maximum intensity and develop- 

 ment in Oligocene, while minor movements continued to 

 Miocene times. 



2. The main elevations of the Rocky Mountains and portions of the 



Andes took place during the Tertiary period, and they were 

 raised to their present height so late as in Miocene and Pliocene 

 times. 



3. Although considerable elevations of the Himalayas are of Pre- 



Tertiary date, the researches of the geological survey of India* 

 show that the special great Himalayan disturbance is of Post- 

 Eocene age ; while in the Sub-Himalayan ranges, there is a 

 large amount of disturbance of Post-Pliocene date.f 



4. The elevation of the main axes of the Alps (although, like the 



others, began earlier) took place in Miocene times, and was 

 prolonged to as late as the Post- Pliocene period, or to the time 

 immediately preceding the comparatively recent Quaternary 

 period. 



It is only necessary to look at the section of any mountain chain to 

 see the enormous amount of squeezing and crumpling the strata have 

 invariably undergone, and the succession of folds of vast magnitude 

 into which they have been thrown. In the Alps there are seven, if 

 not more of these great folds, each constituting a mountain chain. In 

 a straight line across they measure about 130 miles ; but, if the strata 

 were stretched out in the original planes, it is estimated that they 

 would occupy a space of about 200 miles. 



Le Conte states that the coast range of California consists of at least 

 five anticlines, and as many synclines so closely compressed that a width 

 of 15 to 18 miles of horizontal strata has been reduced to 6 miles. 



* Medlicott and Blanford's " Greology of India," pp. 569, 570. 

 f It is a question even whether the earth movement along this great axis of eleva- 

 tion has yet "wholly ceased. 



