164 



FIELD COLUMBIAN MUSEUM ZOOLOGY, VOL. VII. 



the valley to the north are composed mostly of this softer material. 

 Even now, in low water, the Lobos River, which drains this valley, 

 rolls along on its bottom a considerable amount of this material, form- 

 ing at its mouth a small though quite typical delta. The valley 

 about and above Moran shows evidence of considerable erosion, and 

 the material carried away forms a large portion of the low land below 

 this city. 



Lake Amatitlan is about 8 miles long, and about 2% miles wide 

 at either end, and % mile near its middle. The fill on which the rail- 



DELTA AT MOUTH OF LOBOS RIVER, LAKE AMATITLAN 



road is built divides the lake into two parts, or two quite similar 

 basins. The upper is the smaller, and near its center is 95 feet in 

 depth. The lower and larger portion is no feet deep. In its nar- 

 rowest portion, both above and below the railroad, the lake is 50 feet 

 deep. 



The bottom of the lake is a quite uniform basin ; the lake is deepest 

 where widest, and the slope from shore line to bottom is everywhere 

 steep and quite uniform. The bottom is covered with a light mud, 

 mixed with the remains of small plant life. At a depth of about three 

 feet this mud becomes somewhat firm, and is a clay-like substance of a 

 grayish-blue color. The bottom at the base of the tules is quite firm, 

 being covered with a light mud, sand, and gravel. 



