276 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 



Quaternary movement has taken place or not. Could the full extent of the 

 recent fault lines be indicated on the map, it is probable that they would 

 form a complicated series of intersecting lines that would embrace nearly 

 the entire area. 



The first feature of general interest that presents itself upon commenc- 

 ing the study of these recent faults, is that they frequently, if not always, 

 follow the courses of ancient displacements that are usually of great magni- 

 tude. They are recent movements of ancient faults. 



The intimate association of thermal springs with recent faults is to be 

 noticed not only in the basin of Lake Lahontan, but throughout the entire 

 area of interior drainage thus fa)- explored. It is also to be noticed that the 

 hottest springs almost invariably occur on the lines of displacement that 

 have suffered the most recent movement. So nearly constant is this corre- 

 lation, that wherever thermal springs occur, other evidences of recent oro- 

 graphic movement are almost always at hand. The suggestion has been 

 advanced in this connection** that the high temperature of the springs is 

 due to the friction of the rocks along the sides of the fault plane. It is the 

 conversion of motion into heat. As, however, the faults result from a pro- 

 found fracturing of the earth's crust, it is evident that any water which finds 

 its way into a fault may descend to great depths and consequently reach 

 regions of high temperature ; it is more than probable, therefore, that tlie 

 springs derive at least a portion of their heat from the internal heat of tiie 

 earth. It is impossible at present to determine how much of the heat affect- 

 ing springs is caused by friction and how much is due to the prevailing 

 high temperature of the earth at great depths. Probably both causes con- 

 spire to produce the results observed. 



The intimate association of the thermal springs of the Lahontan basin 

 with recent displacements may be illustrated by comparing Plates VIII and 

 XLIV, which will show that but a very few thermal springs occur in this 

 area that are not closely associated with recent faults. 



The various lines of recent displacement in the Lahontan basin have 

 so many features in common that it is unnecessary to enter into a detailed 

 description of each. All that are represented on Plate XLIV, within the 



SM Third Aunual Keport U. S. Geological Survey, p. 232. 



