ORIGIN OF LAKE BASINS. 25 



depressions, each one the record of the piercing of its surface and the 

 burial within its crust of a planetary mass previously revolving independ- 

 ently in space, the date of the last of the catastrophes which pi-oduced 

 that condition must have been so remote that erosion has removed all 

 surface evidence of the fact. Still farther negativ-e evidence may be cited, 

 inasmuch as no buried meteoric masses recognized as such, have Ijeen 

 found in the rocks now forming the earth's surface. This is not proof, 

 however, that the meteoric h^-pothesis, as apjjlied to the earth, is not true, 

 as the main events in that drama are assumed to have been enacted before 

 the formation of the stratified rocks now recognizable. 



Basins due to earthquakes. — During earthquakes there are undula- 

 tions of the surface of the regions affected which sometimes produce per- 

 manent elevations and depressions and thus affect the drainage. The 

 passage of earthquake Avaves through loose deposits ma}- cause them to 

 become more compact and perliaps produce depressions on their surfaces. 

 In these and probably other ways, basins may be formed by earthquakes 

 and grive origin to lakes. 



The best examples of lake basins in America, resulting directly from 

 earthquake shocks, occur in what is known as the " Sunk country "' in 

 southeastern Missouri and northeastern Arkansas. A series of severe 

 disturbances, known as the New ^Madrid earthquake, affected that region 

 between 1811 and 1813, and caused both elevations and depressions in 

 the forest-covered flood plain of the Mississippi. This region has recently 

 been examined by W J McGee,^ who reports that a low dome some 20 miles 

 in diameter, was upheaved athwart the course of the ^Mississippi and that 

 tlie river was held in check for a brief period, but soon cut a channel 

 llirough the obstruction. An adjacent area some one hundred square 

 miles in area, was depressed and is still, in part, occupied by lakes in Avhich 

 the trunks of trees killed by the inundation are standing. 



During earthquakes in regions occupied by unconsolidated rocks, 

 water is sometimes forced to the surface with great violence, probably on 

 account of the compression of porous, water-charged strata, and rises 

 fountain-like above the surface. The water brings with it (juantities 

 of sand and mud which are deposited around the points of discharge and 

 serve to enlarge the depressions produced by the violent outrush. When 

 the fountains cease to play these small crater-like basins i-emain as ponds. 



^ "A Fos.sil Eartliquakc," in Gcol. Soc. Aui., Bull., vol. 4, pp. 411-415. 



