GEOLOGY AND MINERALOGY. 
161 
above the sea-level, and the horizontality of most of the beds, 
show that the elevating force was small compared with that of 
Mexico north, or of Guatimala south. The soundings at the 
mouth of the Coatzacoalcos are the same now as they were when 
examined by direction of Cortes in 1520; so that, for three 
hundred and thirty-two years, there has been no elevation of the 
land here. Every thing on the Isthmus bears, the mark of sta- 
bility, and the absence of any active volcanic force. This is a 
point of great importance where the stability and permanence 
of large buildings are concerned ; and in this respect, this portion 
of Mexico is less liable to motions of the ground than Guatimala 
or Nicaragua ; in which latter place several alterations of level 
have taken place lately. Previous absence of upheaval and 
eruption through a long period of time is a priori evidence of 
the nonexistence of the upheaving cause ; and this is the actual 
condition of the Isthmus of Tehuantepec. 
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