l62 



FIELD COLUMBIAN MUSEUM ZOOLOGY, VOL. VII. 



many times during the past centuries, and to have been responsible 

 for transporting much of the material which has filled up about two- 

 fifths of the lake. The material worn from the mountains by rain has 

 been transported by the inlet and other small streams to the lake, form- 

 ing that portion of the low land bordering it to the north and east. 



LAKE AMATITLAN FROM ITS UPPER END 



This land has so encroached on the lake that now it is narrowest near its 

 middle, where it is only one-fourth of a mile wide. The bottom at this 

 place is of soft mud, apparently to a considerable depth. This is evi- 

 dent from the fact that much trouble was experienced in making a fill 

 across this narrow portion for the railroad. This fill sank out of 

 sight as soon as the soft material of which the bottom of the lake is 

 composed became overloaded. It required much more material to 

 make the railroad fill than the depth of the water indicated. 



To the northwest, the mountains consist of hard granite rock and 

 basaltic columns. The other mountains about the lake are mostly 

 composed of loose material, much of it being volcanic ashes, pumice, 

 and other soft material, which is easily eroded. The hills which border 



