The M 'est American Scientist. 153 



obsidian, or volcanic glass, which has resulted from the rapid 

 cooling of a perfectly fused, igneous rock. From this, great 

 blocks have fallen and accumulated at its base in a talus slope, 

 over which has been built what is popularly known as the glass 

 road, the material of which it is made, being as true a glass as 

 any artificially produced. The colors and structure of this nat- 

 ural glass not only make it the most interesting rock the visitor 

 will find, but the phenomena of its occurrence in this locality are 

 of special scientific importance. 



What was the original thickness of this lava sheet it is not 

 possible to say. The dense glass or obsidian forming the lower 

 portion is from seventy-five to one hundred feet thick; the porous and 

 pumiceous upper portion has suffered more or less erosion, which 

 was in part the result of ice action, the evidence of glaciation be- 

 ing more marked along the lower western slope of the plateau 

 than on the top of it. The surface of the plateau is mostly pum- 

 ice, with little, if any glacial debris scattered over it; but along 

 the western slope the rock has been worn down to the massive 

 obsidian, and the top of the cliff is covered with planed and 

 striated glacial drift from a great variety of sources. 



Haifa mile southeast of Obsidian Cliff, on the plateau, about 

 five hundred feet above the level of Beaver Lake, is a circular pit 

 one hundred feet deep, the mouth of it being three hundred feet 

 wide by three hundred and fifty feet long; its sides stand at an an- 

 gle of thirty-five degrees and appear to be formed of pumiceous 

 obsidian, the angular masses in the bottom being pumice. The 

 rim of the pit does not rise above the level of the surrounding 

 surface, and one comes upon it quite unexpectedly in the timber. 

 The general appearance is that of a small crater which has been 

 but slightly affected by glaciation. 



In the Solfatara Creek valley, the lava flow is exposed in a 

 cliff the lower portion of which is black and red obsidian. 



CONTRIBUTIONS TOWARDS A LIST OF THE 

 FAUNA AND FLORA OF WET MOUNT- 

 AIN VALLEY, COLORADO. 



(Compiled for the Colorado Biological Association.) 

 Ill ALGjE. 



The locality cannot be said to be rich in forms, although the 

 irrigation ditches and creeks yield a certain number of species. 

 Most of the species are of general distribution elsewhere. For 

 identification we are greatly indebted to the Rev. F. Wolle, 

 while one species was kindly named by Dr. W. G. Farlow. 



1. Conferva vulgaris, Rab., near Ula. 



2. Cladophora glomerata, Kg., well distributed; also found in 

 Pueblo Co. 



3. Mesocarpus scalaris, DeBy. , near Ula. 



4. Hyalotheca disilliens. 



5. Draparnaldia plumosa, in Swift Creek, over 8,000 feet alt. 



