18S9.] BOTANICAL GAZETTE. II9 



proved, upon microscopic examination, to consist of the dried 

 remains of these same diatoms, and it is quite evident that 

 this diatom ooze is forming a bed of diatomaceous earth. Sub- 

 sequent investigation proves that a diatom ooze, consisting 

 of the same species, forms the chief constituent of similar 

 marshes all over the park. 



It has also been found that the meadows of the geyser and 

 hot spring basins were once marshes of this character, and 

 are underlaid by beds of soft straw-colored or gray material 

 which consists of the partially dried remains of diatoms. 

 This material when dried is white, loosely coherent, soils the 

 ringers, and consists either entirely or very largely of diatom 

 tests. A number of specimens of this material collected from 

 the Norris, Lower and Upper Geyser Basins, and the hot 

 spring areas of Pelican Creek, were examined by Dr. Wolle, 

 and found to consist of the species already named, forming a 

 diatomaceous earth that is sometimes very pure, and some- 

 times mixed with more or less glassy silica formed by the 

 drying of the siliceous jelly with which these organisms so 

 often surround themselves. 



These diatom beds cover many square miles in the vicinity 

 ot active or extinct hot spring vents of the park, and are 

 often three feet, four feet and sometimes five to six feet thick. 

 The wagon road leading to the geyser basins crosses sev- 

 eral meadows of this character, notably immediately south 

 of the Norris basin, Geyser meadows, and the meadows of 

 the Upper and Lower basins of the Firehole. At these places 

 the beds are exposed in the cuttings made, for drainage, and 

 square blocks of the dried diatom earth lie scattered about at 

 the sides of the road. 



In most of the cases observed, these diatom marshes cover 

 ancient deposits of siliceous sinter, diatoms growing in the 

 cooler waters of the decaying springs or their overflow, and 

 covering the sinter beds until even the tops of the cones are 

 submerged beneath the ooze and the vegetation it supports. 

 This is actually the case at several places in the Lower Fire- 

 hole Geyser Basin, and at the Lewis Lake and Pelican Creek 

 hot spring areas. Such marshes also occur, however, where 

 the cooler alkaline waters of the geysers and boiling springs 

 overflow the natural surface of the ground. 



The diatom ooze thus far observed is from cool or tepid 



waters, but in the collection of , algae from the hot springs of 



the park, and placed in the hand of Prof. W. G. Farlow for 



tudv and description, specimens of Denticula thermalis (Kg.) 



