GEOLOGY OF SOUTH WES TEEN IOWA. 331 



Madison and Adair. Like the greater part of the counties 

 of the second tier, it is three townships in width from north 

 to south, and four in length from east to west. It is thus a 

 true parallelogram, containing four hundred and thirty -two 

 square miles or two hundred and seventy-six thousand four 

 hundred and eighty acres. 



Drainage and Surface Characters. With the exception of 

 half a dozen square miles of the extreme northeastern corner, 

 which are drained into Clanton's fork and thence into the Des 

 Moines, the whole of Union county is drained by the tribu- 

 taries of the Missouri river, principally by Thompson's fork 

 of Grand river. This stream, together with its branches, has 

 a general course through the county from northwest to south- 

 east. It will be seen that the Great Watershed which 

 divides the drainage between the two great rivers, passes 

 across the extreme northeast corner of Union county, yet 

 the highest land of the county is not there ; but upon a 

 secondary watershed, that which divides the drainage of 

 Grand and Platte rivers. 



The profile in the first part of this report, prepared from 

 notes of Mr. Thielsen, Chief Engineer of the Burlington and 

 Missouri River Railroad, shows that Highland, near the center 

 of the county, is the highest point on the line of the road 

 between the two great rivers, being seven hundred and ninety- 

 four feet above low water in the Mississippi at Burlington, and 

 twelve hundred and eighty feet above the level of the sea. 

 The lowest point along the line of this road within Union 

 county is in the bed of Grand river, which is about three 

 hundred feet lower than the surface at Highland. The valley 

 proper of Grand river, however, is only from one hundred to 

 one hundred and fifty feet deep from the general level of the 

 upland in its neighborhood, and the great height attained 

 at Highland is by a gradual rise of the general surface from 

 the vicinity of Grand river valley. 



The valley of Twelve Mile creek, the principal branch of 

 Grand river, in this county, has a similar average depth and 

 character, but it has no exposure of strata along its entire 



