CHAPTER XLVI. 

 PHYSICAL GEOGRAPHY. 



IGNEOUS ROCKS LAND AND WATER SPRINGS, WELLS, AND GEYSERS 



SNOW AND ICE THEIR EFFECTS. 



IN the foregoing pages we have chiefly considered the stratified rocks, but 

 we are now approaching another branch of our subject viz., " Physiography," 

 which, as distinguished from the usual so-called Physical Geography, will 

 deal with the phenomena of the earth, air, and water, thus leading us to 

 Meteorology as a conclusion. 



We have arrived at a certain knowledge concerning the Earth as a 

 planet, her place in the universe, and the composition of the " Crust," as it 

 is termed. We have examined the stratified rocks, which include sand and 

 gravel, stones, and boulders equally. To a geologist they are all " rocks." 

 We must now examine the igneous rocks, which bear an important part in 

 the structure of the Earth, whose surface we have now more minutely to 

 examine. It has already been stated (p. 5 71) that igneous rocks have been 

 upheaved while in a state of fusion that is, while in a melted condition. 

 These igneous, or fire-produced rocks, are divided into classes, just as the 

 unstratified rocks are, . and the divisions are called the VOLCANIC and 

 PLUTONIC, including " Basic" and " Acidic," according as they are possessed 

 of less silica or more. 



, Sometimes the igneous rocks are classed as volcanic, trappean (from 

 trappa, a stair, such as in the Giant's Causeway), and granitic. The volcanic 

 in such case being the modern or upper rocks, such as lava, scoria, etc., which, 

 having been cast up by volcanoes, are of comparatively recent formation. 



The VOLCANIC rocks, then, are of recent date, comparatively speaking ; 

 they form the constituent portions of the volcanoes of the present day, and 

 are found as basaltic formations. They are traced as far back as the 

 Tertiary period of the glojpe. Amongst the volcanic rocks we find basalt, 

 augitc, porphyry, serpentine, pumice, pitchstone, felspar, etc. But no 

 doubt volcanic action has been going on ever since the beginning of the 

 world as it is now, and will continue to do. It is somewhat curious that 

 the very old igneous rocks should not be more evident. 



The PLUTONIC rocks do not differ essentially from the foregoing. 

 There is less quartz and more hornblende ; and if the ages during which 

 these formations -have been existent in the earth-depths after they became 



