HOLMES.] OBSIDIAN CANON. 31 



fragments and lined by huge angular masses of black and banded ob- 

 sidian rock. From the upper border of the debris slope the vertical cliffs 

 rise to the height of nearly 200 feet. The lower half is composed of a 

 heavy bed of black obsidian, which exhibits some very fine pentagonal 

 columns, somewhat irregularly arranged and frequently distorted, but 

 with perfectly cut faces that glisten in the suidight. The upper portion 

 of the wall is comi30sed of a much more obscurely columnar mass of im- 

 pure spherulitic obsidian, the rude faces of the columns being often as 

 much as 10 or 12 feet across. To the right and left the columnar char- 

 acter becomes less marked, both in the upper and lower part of the cliff, 

 and farther out seems to be entirely lost, the glassy rocks grading into 

 the gray sanidin trachytes and obsidian porphyries of the surrounding 

 hills. 



Extending upward from the edge of the promontory in a moderately 

 genl le slope are 400 or 500 feet of obsidian strata that exhibit some most 

 interesting characters. There is no heavy mass of pure glassy rock, but 

 a succession of irregular layers of a dozen or more varieties of spheruli- 

 tic obsidian, obsidian porphyries, and breccias. The colors of these 

 rocks are exceedingly varied, the prevailing blacks giving way to reds, 

 browns, greens, and the richest possible marblings and mottlings. 



One of the most striking characteristics of these rocks are the spher- 

 nlitic concretions which occur to a greater or less extent in all the 

 varieties. These bodies seem to prevail in the ashy-like bands or lay- 

 ers which, in the more compact mass toward the base, are frequently 

 contorted, giving the rock the appearance of a banded and contorted 

 gneiss. The ashy-appearing layers are probably composed of the sam.e 

 material as the concretions, since when we split the rock with the bands, 

 the surfaces of the gray bands next the glassy laj^ers are simply a con- 

 nected or coalescent series of nodes or hemispheres, which have the 

 usual appearance of the more isolated concretions. Where the concre- 

 tions are scattered throughout the glassy mass, they are globular or 

 composed of a cluster of globes. They have, in most cases, a distinctly 

 radiated structure, with not infrequent^ concentric layers near the sur- 

 face. The interior is gray or pinkish-gray, and the surfaces pinkish or 

 liesh-colored. 



In the coarsely columnar part of the wall the spherulites are often 

 a foot or more in diameter, and appear much flattened and distorted. 

 It is probable that these irregular forms are produced by the coales- 

 cence of a large number of smaller ones, as there are apparently many 

 centers of radiation. Large beds of the rock seem to be made up al- 

 most wholly of the concretions, and, where decomposed, a mass of 

 coarsely cellular or honey-combed obsidian remains. The brecciated 

 beds consist of ^an ashy matrix, in which are imbedded angular frag- 

 ments of every variety of the brilliantly-colored spherulitic and ordin- 

 ary obsidians. 



The collection of hand specimens made at this place is very complete, 

 numbering upwards of three hundred. Their examination by special- 

 ists in petrography will doubtless develop many new and interesting 

 features, as no equally rich deposit of similar rocks has heretofore been 

 brought to their notice in this country. 



Indian implements. — It occurred to me, while making examinations 

 at this point, that the various Indian tribes of the neighboring valleys 

 had probably visited this locality for the purpose of procuring material 

 for arrow-points and other implements. A finer mine could hardly be 

 imagined; for inexhaustible supplies of the choicest obsidian, in flakes 



