Il8 BOTANICAL GAZETTE, [May, 



the immense beds of Tertiary age, which occur in many 

 parts of the world. 



In the prosecution of geological work in the Yellowstone 

 National Park, the writer has found that diatom beds of re- 

 cent origin cover many square miles in the vicinity of the 

 geyser and hot spring basins. These deposits, which are 

 among the largest fresh water diatom beds of contemporary 

 age known, are still forming by the growth of diatoms in the 

 warm water marshes supplied by the hot spring waters. 



These diatom marshes are sure to be remembered by all 

 who may attempt to cross them, for the treacherous surface 

 and apparently bottomless depths of the ooze offer an effectual 

 barrier to any progress in that direction. 



Near the Emerald springs at the Upper Geyser Basin of 

 the Firehole river, the most noted geyser region of the park, 

 there is a typical marsh of this character. The waters hav< 

 in times past encroached upon the neighboring patch of 

 timber, killing the pines (Pinus Murrayana), whose bare, 

 gray trunks stand upright in the ooze or lie scattered about 

 half immersed beneath the waters of the marsh. A subse- 

 quent partial recession of the water has left a bare, white 

 strip between bog and wood, on which vegetation has as yet 

 a feeble hold, and the gaunt poles of the dead pines stand in 

 a white powdery soil that is evidently a dried portion of the 

 marsh mud. A large part of this ~bog is covered with a 

 sparse growth of brackish water plants, and the drier parts 

 are grass grown and form a fairly firm meadow bottom. The 

 greater portion consists, however, of a semi-liquid, greenish 

 gray, dirty looking ooze. Under the microscope this was 

 found to consist of beautiful siliceous tests of various species 

 of diatoms. Samples of this material, which Mr. Francis 

 Wolle has kindly examined for me, were found to contain 

 the following specie 



Denticula valida Epithemia hyndmannii 



elegans Cocconeraa cymbiforma 



Navicula major Achnanthes gibber ula 



viridls Mastigloia smithii 



Epithemia argus Fragillaria 





a u 



var amphicephala 



The first species named, Denticula valida, was the most 

 abundant, forming the bulk of the specimen. It may be of 

 interest to note here that this species has been found in the 

 gatherings from the geyser basins of Iceland. 



The white pulverulent material at the margin of the bog 



