BEDDED OE STBATIPIED BOOKS 49 



available nucle-us, in this case the grains of calcareous sand npon 

 the bottom. Thus are gradually built up beds of no inconsid- 

 erable thickness, such as the well-known Carboniferous oolitic 

 limestones of Indiana and Kentucky. The microscopic structure 

 of stones of this class is shown in Fig. 7 on p. 105. 



Rocks which were laid down in the manner just described, 

 whether composed of inorganic particles or fragmental materials 

 from marine and fresh water organisms, are designated as 

 sedimentary. They occur in more or less well-defined heds or 

 strata, and hence are spoken of as bedded or strait fled. Owing to 

 the fact that they have in most cases been deposited in com- 

 paratively shallow water, they retain the superficial markings 

 made upon them by waves and other agencies prior to their final 

 consolidation. 



Such naturally lie approximately horizontally where not sub- 

 sequently disturbed by earth movements. The earth's crust, 

 however, is by no means in a state of stable equilibrium, but, 

 being subjected to continuous stress or compressive force, is 

 often broken, crushed, or folded, and crumpled to an extra- 

 ordinary degree. The name faidt is applied to the profound 

 fractures made by these movements, which, inclined at various 

 angles to the horizon, may extend for miles. Usually the rocks 

 on one side of a fault will be found to have sunk down, while 

 those of the other remain stationary or are raised, producing 

 thus an inequality of surface that may assume mountainous 

 proportions. Most mountain ranges, in fact, are due to a com- 

 bination of faulting and folding processes. It not infrequently 

 happens that the masses of rock, sliding over one another along 

 a line of fault, produce smooth or striated and often highly pol- 

 ished surfaces, to which the name sUchensides is given. Such 

 are particularly noticeable among serpentinous rocks, being ap- 

 parently due to motion generated in the mass by increase in 

 bulk incident to its conversion into serpentine.^ The name vein 

 is given to rock masses of chemical origin, deposited along pre- 

 viously existing fractures which may or may not be true faults. 

 By some authorities the name is also made to include the smaller 

 injections of igneous rocks. Such are here classed under the 

 head of dikes. It is customary to divide the veins into two 

 classes: (1) the mineral veins, in which the materials have 



^ See On the Serpentine of Montville, New Jersey, Proc. XJ. S. National 

 Museum, 1888, p. 105. 

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