WANLESS— LITHOLOGY OF WHITE RIVER SEDIMENTS. 191 



then treated with dihite hydrochloric acid until no effervescence fol- 

 lowed the addition of more acid. The residue was then washed and 

 dried at iio° C. and weighed, the difference representing the quantity 

 of soluble cement. The residue was then placed in a beaker and 

 water added to a level 9 cm. above the base of the beaker. This was 

 allowed to stand 10 minutes, in which time all particles with a density 

 of quartz or greater and a diameter greater than o.oi mm. settled. 

 The liquid with the mud was decanted and this process was repeated 

 until the liquid was clear at the end of 10 minutes. The residue was 

 then dried and weighed, the difference in weight representing the 

 amount of mud in the sample. The residue was then decanted to 

 remove silt. The sediment was covered with 14 cm. of water and 

 allowed to settle for 20 seconds and decanted. This decantation was 

 continued until the liquid was clear, some of the silt being saved for 

 examination. The particles thus separated as silt have diameters of 

 0.01 to 0.1 mm. All coarser residues, when dried and weighed, repre- 

 sented the sand content of the sample. 



In samples containing a noticeable percentage of heavy minerals, 

 the sand residue was treated in a separatory funnel with Thoulet's 

 solution (mercuric chloride and iodide dissolved in water) of a density 

 of 2.95-3.0. By this method the rarer heavier minerals were concen- 

 trated and their amount and variety determined. From the heavy 

 concentrate the magnetite was removed by an ordinary horseshoe 

 magnet, and it was found that a fair concentrate of micas for study 

 purposes, without attempt at quantitative separation, could be made 

 by sliding the lighter sands repeatedly from a sheet of paper, where 

 the mica flakes generally remained on account of their flatness. 



The sands, silts, and heavy concentrates were then studied micro- 

 scopically, with a series of liquids of known indices of refraction, and 

 the individual minerals thus determined. 



IV. Types of Sediments. 

 In the sequence of sediments composing the White River series 

 there are: (i) Stream-channel sandstones, represented by those of 

 the Protoceras, Metamynodon, and Titanotherium levels whose rela- 

 tions to the surrounding clays can, generally, be easily deciphered. 

 Due to the superior resistance to weathering of the sandstones, the 



