98 KANSAS Academy of Science. 



saccharoidal gypsum of Marshall county, outcropping on the banks of the Big and 

 Little Blue, a few miles above Blue _Rapids, is fully 250 feet lower in the geological 

 scale than the gypsum near Geuda, and corresponds with an horizon of gypsiferous 

 shales in the Permo-Carboniferous beds which are just below the lowest strata that 

 outcrop in the railway cut at Fort Riley. 



The largest of the northern salt marshes, and probably the largest in the State, 

 is the one on Marsh creek (No. 6 in the list). Its lowest part is in section 4, town 

 5, range 5, W., and it has more than half of section 5, and stretches into three 

 sections of town 4, and into some part of range 6. It is seven miles long, and in 

 one place it is quite a mile across. Like the Tuthill marsh, its area has been re- 

 duced since the settlement of the region, and from the same cause, but its large 

 areas of saline efflorescence, resembling snow-covered fields, are remarkable objects 

 in the extensive views obtained from neighboring uplands. The marsh itself is 

 below the level of the alluvial bottom. In places the alluvia form steep walls of 10 

 to 15 feet high, bounding the lower saline slopes, but elsewhere the alluvia have 

 all been washed away, and the marsh slopes up to thin, sedimentary soils, formed of 

 the shales and harder beds that constitute the geological bed-rock, and from which 

 the marsh derives its salt. These shales are at the top of the Dakota formations, 

 and wells sunk just outside the marsh, at higher levels, penetrate the highest Da- 

 kota sandstones, and these are seen in outcrop only a mile to the south. On the 

 N.W. } of section 5, town 5, range 5, some years ago, a well was bored fifty feet 

 deep within the borders of the marsh. It gave an artesian flow of brine, which, 

 though partially choked, is still running. Its strength on the salimeter was 14°, 

 which is exactly the strength of brine taken from a hole six feet deep on the 

 Tuthill marsh the day before. It was believed by the well-borers that a stream of 

 fresh water diluted this flow of brine. The tops of the slopes, on all sides of the 

 marsh, are crowned with the Benton limestones. Wells near by penetrate black shale, 

 the analogue of the lignite bed of the upper Dakota, which, near Tuthill marsh and 

 other places of the region, is worked for fuel. The bed of the marsh, in wet sea- 

 sons, is a dangerous black bog. At the dry time of our visit it was safe, but soft to 

 the foot. 



There are two marshes on Salt creek, in Mitchell county (No. 4 of the list), dif- 

 fering little from the one just described, except that in both, the alluvia, forming 



F'G. IV. Seciion on a branch of Salt Creek, 



f/litchell Co., Kas. 



100 ft. 



50 ft. 



vertical walls to the creek and marsh, are much thicker, being 15 to 20 feet in 

 thickness; and in the larger marsh there are two vertical outcrops of Dakota sand- 

 stones, in one of which is a salt spring, and Benton shales are exposed at less than 

 25 feet above the highest exposure of Dakota formations. 



In no essential particulars do any of the marshes (3 to 7 in the list, inclusive), 

 eight in all. differ from the descriptions already given. The salt is in each case 

 derived from shales of the Upper Dakota, so there is no connection with the salt- 

 rock horizon which came at, or just after, the close of the Permo-Carboniferous 

 period. 



