SUKFACE FEATTJEES. 31 



It will be readily understood that profiles on so small a 

 scale as that npon which these are drawn npon the accompa- 

 nying sheet can do no more than to give an approximate 

 outline of the surface, which indeed is all that they are 

 intended to do. The difficulty also of constructing such 

 profiles from the independent notes of so many different 

 persons will be understood. Mr. Morley says, in explana- 

 tion of his work: 



"la preparing these profiles, I have used as far as practicable the elevations 

 just as they were given by the different railroad surveys,, but in some cases I 

 have been obliged to depend upon other data. Much of this was furnished by 

 yourselt and Prof. St. John, and the remainder was calculated from the known 

 slopes of rivers and watersheds. The elevations west of the Great Watershed 

 which were furnished by the railroad engineers, for the most part run down some 

 river valley instead of keeping on a direct line across the State, 'lo follow these 

 would not give a correct idea of the general elevations of the summits between 

 the streams, I have, therefore, been obliged, to some extent, to use other data in 

 determining general elevations of the surface in such cases. 



In profile JNo. 1, a part of the elevations are from railroad surveys, but the 

 greater part are from data furnished by the Geological Survey, and by estimates 

 from kuown river slopes. There are, however,, enough accurately known eleva- 

 tions to insure a fair degree of accuracy along the whole line.. 



In profile No. 2,, we had a continuous line of levels from Dubuque to Sioux 

 City, furnished by Mr. J. E. Ainsworth, and also another line from Fort Dodge to 

 Sioux ^ity by a different route, furbished by L.. Burnett. Use fias been made of 

 both of these, and the whole profile is constructed from them except that portion 

 of it between the Floyd and Big Sioux rivers.. This part of the line was, as in 

 the case of the others also, produced directly westward from. Floyd river instead 

 of following down its valley to Sioux City. 



La profile No. 3,. the elevations are obtained from surveys made by the Cedar 

 Rapids and Council Blufis Railroad Company (now the Chicago and .North- 

 western.) These elevations are those of the located line of that company from 

 Clinton to the Boyer river, where instead of following down its valley as the 

 road now does, the profile is continued directly westward to the Missouri river. 

 I was enabled to do this by the aid of notes of a former survey made by Mr. C 

 W. Irish in the interest of the same company. 



Profile No. 4,, was constructed from Davenport to Cass county from notes 

 furnished by the Chief Engineer of the Chicago, Rock Island, and Pacific Rail- 

 road. In Cass county, the roaci bends much to the northward, and again, soon 

 after, almost directly southwestwarcl, but the profile is continued directiy west- 

 ward in order to show the contour of the country along a line running across the 

 streams nearly at right angles with their course. That portion of the profile 



