716 DYNAMICAL GEOLOGY. 



these minerals, just as they are in veins. Most of the species in amygdaloidal 

 caTities are hydrous, — showing that they were formed at a much lower tempera- 

 ture than the materials of a granitic vein ; and some of them may perhaps he 

 formed even at the ordinary temperature. "When several species occur in suc- 

 cessive layers together, the uppermost, or latest formed, usually contain the 

 most water in their constitution, — silica and calcite excepted, which are not 

 hydrous species, and may occur at the top or bottom, or any part, of the series. 

 At Plombieres in France, the cement and brick of walls of Roman origin have 

 become penetrated in places with zeolites through the action of the water of a 

 warm (140° to 160° F.) mineral spring (Daubree). 



VI. MOVEMENTS IN THE EARTH'S CRUST, AND 

 THEIR CONSEQUENCES. 



The topic under consideration in this chapter is the origin of the 

 movements in the earth's crust or mass, and the methods by which 

 their results have been brought about. These movements and then* 

 consequences include (1) Changes of position and level; (2) Frac- 

 tures, faults, and structural peculiarities produced in rocks ; (3) 

 Earthquakes ; (4) Evolution of the earth's great outlines and reliefs, 

 and of the successive phases in geological history. 



1. CHANGES OF POSITION AND LEVEL. 



Changes of position may take place either horizontally or verti- 

 cally, or in both directions simultaneously. 



1. Causes of change. 



Some causes of local change have already been mentioned : — 



1. The undermining of strata by the 



eroding action of subterranean waters (p. „__,... °' ... ..' 



649). 



2. The loeight of a superincumbent 

 mass of horizontal deposits on wet beds 

 of clay or sand, producing a lateral 

 movement, and also an extrusion if 

 the case admits of it (p. 649). — The 

 laminated clay-layers often become 

 plicated by the pressure, while the 



* J . Plicated clayey layer. 



beds between which they lie are 



only slightly compacted or are unaltered. Fig. 977 is a reduced 

 view of a layer thus plicated, from the Post-tertiary of Boonville, 

 N.Y. Vanuxem, who mentions the facts in his New York Geolo- 



