THE CRUST OF THE EARTH 179 



Granite is the most common igneous rock. It is of 

 coarse structure and is made up of small crystals of 

 quartz, feldspar, and mica, which can be plainly seen and 

 distinguished. Granite may be gray, red, or pink, varying 

 according to the color of the feldspar. It is one of the 

 hardest and most durable of rocks. It forms a part of most 

 mountain chains; in the wearing down of old mountains, 

 it is often left exposed, sometimes standing in peaks, like the 

 White Mountains and the Sierra Nevadas. The rocks of 

 the New England coast show that granite underlies much 

 of that region. 



Granite is used for the foundations and walls of buildings, 

 and for bridges, paving blocks, and monuments. Maine has 

 long been supplying granite to the country, in many 

 varieties of color. All the New England states have large 

 quarries. 



Lava is a fine-grained igneous rock which varies greatly in 

 color. Vesuvian lava is very dark; the lavas on the west 

 slope of the Rocky Mountains are light, of reddish-gray color. 

 In the eastern states the lava, which is called trap rock, is a 

 dark bluish-gray and contains a compound of iron. Mount 

 Holyoke in the Connecticut Valley in Massachusetts and 

 the Palisades of the Hudson opposite New York City are 

 ridges of hard trap rock. 



203. Sedimentary Rocks. Sedimentary or fragmental 

 rocks are formed from fragments broken and worn off from 

 older rocks by the action of frost, waves, and wind. These 

 fragments are carried by streams and ocean currents until 

 finally, in quiet water, the sediment falls to the bottom, form- 

 ing horizontal layers. The finer fragments, being lighter, are 

 carried farther from shore and thus the fragments are as- 

 sorted according to size. These fragments, in the course 

 of time, are cemented together in great beds or sheets. 

 These are called strata, which is the plural of the Latin word 

 stratum, meaning "a bed." .- 



