and Orography of the Earth's Surface. 5 



contrary, the lower, even when submarine, the motions are, 

 the more difficult, and its effects more local. For in this 

 resides probably partly the difference between the present 

 and the former activity of volcanoes. These have lost very 

 little or nothing of their former exciting cause, but only the 

 secondary circumstances of their possible expansion by this 

 force have been modified by time. 



Let us continue our approximative estimation of the Heights 

 of Chains in the primitive periods, according to the mentioned 

 depths of the various seas at different times ; the highest 

 hills in the Primary period would be between 1500 to 2000 

 feet, in the Zechstein period already 3000 to 4000 feet, in the 

 Trias time 4000 to 5000 feet, in the Jura period 5000 to 6000 

 feet, in the Chalk time 6000 to 11,000 feet, in the Tertiary 

 period 8000 to 20,000 feet, and in the Actual, 10,000 to 

 26,000 feet. The middle value of these highest pinnacles 

 would be for the period of the Trias and Jura about 4000 feet, 

 in the Chalk period 8000 feet, in the Tertiary period 10,000 

 feet, and now it would be 12,000 feet. 



The mountains next in height would have increased in 

 extent from the oldest times till now, as well as the inclined 

 planes under the sea level. The greatest height of those 

 chains may have attained in the Trias already 3000 feet, in 

 the Jurassic period about 4000 to 5000 feet, in the Chalk 

 period 6000 to 8000 feet, in the Tertiary time about 4000 to 

 30,000 feet, and now they measured 6000 to 12,000 feet. 

 Their middle value would give only 2000 feet in height for 

 the Trias period, 3000 for the Jurassic, 7000 for the Chalk, and 

 8000 for the Tertiary one. 



The greatest height of the hilly countries may have been 

 in the Primary period 1000 feet, in the Zechstein 1500 feet, 

 in the Trias 1600 to 1800 feet, in the Jurassic 2000 feet, in the 

 Chalk 2500 feet, and in the Tertiary at least 3000 feet. Their 

 middle height which varies now between 1500 and 3000 would 

 have attained in the primary times only 600 feet, in the 

 Zechstein period 1000 feet, in the Trias 1500, in the Jurassic 

 1000 feet, in the Chalk 2000 feet, in the Tertiary time 2500 

 feet, and in the Alluvial 3000 feet. 



