BIRDS OF MARSHALL COUNTY 



125 



A small section of the northwestern corner of the county lies 

 within the Wisconsin drift area. However, most of the marshes 

 and "kettle holes" which characterize that formation have now 

 been drained. The lowan drift sheet extended over the north- 

 eastern corner and as its most characteristic work left sr-attered 

 bowlders, some of which are of hu.sre size. The remaind:r of the 

 county is covered with a loess soil, which has eroded into rolling' 

 hills separated by narrow V-shaped valleys. The most important 

 physiographic feature from an ornithological standpoint is Towa 

 river. It has a general northwest to southeast trend and serves 



Fig. 12. Characteristic low timlier of Iowa river valley. The two old 

 elms represent the older timber growth which is now largely cut off. 



as a bird-migration route to the interior of the state. The val- 

 ley averages from one to two miles in width and contains more 

 or less timber. At various places in the county cut-offs have 

 been formed, some of which still contain permanent bodies of 

 water, while others are filled by the spring freshets and then 

 slowly disappear by evaporation during the summer months. 

 The Goose Pond or Ponds, frequently menttoned in this paper, 

 is the largest of these and lies northwest of Marslialltown. It 

 consists of a pond or series of ponds, depending on the state of 



