IOWA ACADEMY OF SCIENCES. 77 



Twice in the short journey from Dubuque to Dyersville, the 

 land forms change with almost surprising suddenness; three 

 distinct topographic areas are included between the eastern 

 and western borders of a single county. 



OBSERVATIONS IN THE VICINITY OF WALL LAKE. 



BY FRANK A. WILDER. 



The Wall lake in question is a picturesque sheet of water 

 three miles long and a mile wide, in southeastern Sac county. 

 The only published observations in regard to this lake that I 

 have found are those of Mr. Charles A. White, who wrote in 

 regard to it in connection with other walled lakes of Iowa, in 

 the American Naturalist, Vol. II, and in the annual reports of 

 the Geological Survey of Iowa, Vols. I and II. 



During the past summer while tracing the course of the 

 Altamont moraine the writer very properly arrived at Wall 

 lake, for it was previously known that the lake lies in the 

 moraine and owes its existence to morainic conditions. The 

 purpose of this paper is to record certain observations that 

 make more definite the history of the lake. Most of these 

 points have been observed before, but the locating of the outer 

 edge of the moraine near Wall lake makes it possible to 

 attempt certain new deductions in regard to its origin. 



A topographic map would show that Wall lake fills but part 

 of an extensive hollow, which at points is lower than the lake 

 itself. The lake is in the form of a letter L, the long bar 

 lying east and west while the short bar extends to the south. 

 Morainic hills of very moderate elevation are found all about 

 it except at its eastern end and along its southwestern shore. 

 At the southwestern extremity the shore line is uncertain, 

 consisting of marshes and low land with barely elevation 

 enough to keep the water from flowing to the south. This 

 low trough extends to the south for two miles, then swings to 

 the west and continues as far as the Boyer river, four miles 

 away. In width it varies from a mile to a mile and a half. It 

 is very level, has no natural drainage, and when visited in 

 June, 1899, water stood abundantly on the surface. For these 

 reasons, and perhaps also on account of the nature of the soil, 

 no attempt is made to cultivate this strip of low land, and it is 



