SURFACE DEPOSITS. 119 



process of deepening the river valleys. For example, one of 

 these deposits occurs almost upon the very brow of the bluffs 

 that border the valley of the Mississippi, near Davenport. 

 This example is one of unusual interest, in consequence of the 

 existence there of an extensive bed of ancient peat which is 

 covered to the depth of several feet beneath the prairie soil, 

 and the discovery in the clay above the peat of the remains of 

 a Mammoth. The accompanying diagram, fig. 4, and the 

 following explanation by W. H. Pratt, Esq., Secretary of the 

 Davenport Academy of Science, shows the position of the 

 deposit in relation to the drift. 



Fig 



The exposure was made by the excavation for the Chicago, 

 Rock Island, and Pacific Railroad Company, previous to 

 which there was no appearance at the surface to indicate the 

 presence there of any thing more than the ordinary Drift 

 Deposit. Mr. Pratt's notes and references to the diagram 

 were obtained while the excavation was fresh. 



" No. 1. The ordinary prairie soil, one foot. The prairie here extends to the 

 edge of the bluff, gently sloping backward towards the north. 



" No. 2. The " yellow clay " or loam, twenty feet thick, iron-stained, frequently 

 distinctly laminated ; laminae curved and have their layers of sand interstratined 

 in some places. It contains small calcareous nodules and shells of the genera 

 Succinea, Relicina, and Pupa. This clay makes good brick. 



" No. 3. Bluish-gray clay, three to five feet thick, not stratified ; contains a few 

 shells like those of No. 2. A tusk, several teeth, and some other portions of 

 Elephas primigenius {?) were found just at the junction between Nos. 2 and 3. 



" No. 4. A bed of brown peat one foot thick, which burns tolerably well. In 

 some places the peat-moss, Hypnum aduncum, was so well preserved as to be 

 recognized. Quantities of much decomposed coniferous wood are distributed 

 throughout this bed. 



