6 M. Ami Boue on the Talceohijdrography 



On the Middle Height of the lowest parts of the Continents f 

 according to Humboldt and Johnston. 



We can limit the estimations for each continent and can 

 draw the conclusion how small that height must have been in 

 the Primitive period. In Europe the middle height gives now 

 only the middle value of 300 feet. As the middle value of 

 the highest chains of the mountains of middle heights of the 

 hilly land in the Alluvial period, is to that in the Primary 

 time about 4 or 5 : 1 in the Zechstein, about 3 : 1 in the Trias, 

 2 : 1 in the Jura, as 2, 2 : 3 in the Chalk, as 2, 3 : 3, and in the 

 Tertiary as 2, 5 : 3, we obtain by using these researches in 

 the middle height of the lowest parts of the continents in the 

 different Primary periods 60 to 80 feet, in the Zechstein 

 period 100 feet, in the Trias 150 feet, in the Jura 180 feet, in 

 the Chalk about 200 feet, and in the Tertiary 250 feet. These 

 values are naturally contrary to those of the cavities of the 

 parts of the sea bottoms which were the nearest to the shores 

 during the different geological periods. 



With the aid of such philosophical collections of heights 

 as Strantz gave us, (Berghaus' Annal, 1830, vol. ii. ; 1832, 

 vol. vi. ; 1835, vol. vii. ; 1836, vol. xiii. ; 1839, vol. xix. ; 1841, 

 vol. xxiii.), one might with some difficulty establish by ap- 

 proximations similar values for the breadth of the chains, 

 the height of the plateaux and cols, the breadth of valleys, 

 the length of the course of rivers, &c. s during the different 

 geological periods. I may only mention one of these, viz., 

 the angle of inclination of the low lands and of the lands of 

 the middle heights for which Strantz adopts for the first 5° 

 to 10°, and the latter 10° to 20°. These values have in- 

 creased always from the older times till now, a fact which 

 shews the necessity to admit in the Primary times not only 

 a much flatter land than now, but quite flat shores. Quite 

 the contrary must have taken place in the chains, because 

 the higher were not protected as now by so many mountains 

 of secondary height ; so that the angle of inclination of these 

 last is much smaller than formerly. Generally this value 

 rises with the smallness of the hill and diminishes with its 

 greatness. But this value of the inclination of the plane 



