762 DYNAMICAL GEOLOGY. 



3. Producing flexures of strata (as in a synclinorium), and thereby making proper 

 synclinal valleys ; but such valleys are generally obliterated afterward by denuda- 

 tion, pp. 749, 750. 



4. Producing monoclinal uplifts, and consequently intervening depressions. 



5. Producing widely opened fractures (a rare occurrence. ) 



IX. Lake Basins. 



1. Through glacial action, the glacier ploughing deep where the rocks are soft, and so 

 making a deep depression, and then ceasing the excavation where there is a change 

 to a hard rock, p. 539. 



2. Through a dam thrown across a valley, by (1) a moraine from a glacier, p. 686; 

 (2) a slide of gravel, or avalanche ; (3) a flow of lava; or (4), of a temporary charac- 

 ter, through damming by a glacier. 



3. Through a dam or dike of sand or gravel made along a seashore, by the waves 

 and tidal currents, shutting off a region of water from connection with the sea, which 

 may finally become fresh, if it receives the drainage of the back country. 



4. Through uplifts of mountains surrounding intervales or low plains, for which 

 subsequent erosion provides no complete drainage. 



5. Through the elevation of a country producing level regions, over which depres- 

 sions remain without a drainage channel, because the waters are too sluggish in move- 

 ment for much erosion, as about the headwaters of the Mississippi. 



6. Through the undermining of the surface deposits of a country by the action of 

 water. 



7. Through the ejection of lavas from a volcano, leaving, when the volcano becomes 

 extinct, a crater as a basin-like depression. 



8. Through the contraction of the rocks beneath a region, in consequence of cooling, 

 causing a depression of the surface. 



X. Markings on Rocks. 



1. Scratches. — 1- By the movement of glaciers, pp. 538, 684; or of icebergs, p. 

 686 ; or of any floating ice, carrying stones at bottom. 



2. By the mutual friction of the opposite walls of a fissure, at the time of the making 

 of the fissure (the usual way), or afterward, p. 90. 



3. By the sliding of beds on one another, either as a consequence of gravity, p. 655, 

 or of lateral pressure, p. 90 



4. By the drifting of sands by winds, pp. 91, 632. 



5. Through the rapid transportation of stones by water. 



6. By land slides. 



2. Of organic origin, as footprints, etc. 



2. Other markings. — 1. Ripple-marks, rill-marks, rain-drop impressions, p. 84. 



XI. Ignkous Action. Earthquakes. 



Pages, 702, 741. 



XIX Change of Temperature. Sources of Heat. 



1. Transformation of motion into heat. — 1- By movements in strata ; 

 probably the principal source in metamorphism, p. 698. 



2. By means of movements in water or air, as in the breaking of -waves on a rocky 

 coast ; very feeble in its action, if at all appreciable, unless in warming slightly the 

 atmosphere. 



2. The Earth's interior heat. — 1. Through escape outward from the earth's 

 interior, p. 699. 



2. Through convection upward into strata, or "a rise of the isogeothermals," in 

 consequence of the accumulation of sedimentary beds at surface, p. 730. 



