318 THE POPULAR SCIENCE MONTHLY. 



stream having access to such, an amount of sedimentary material 

 that for a time it filled up rather than eroded its channel. Ap- 

 parently the conditions favorable to such effects would be most 

 readily furnished during the Glacial period, when the streams of 

 that region were swollen not only with the increased annual pre- 

 cipitation, but with the melting of the glaciers which doubtless 

 had for a long time occupied the mountains near the head-waters 

 of the Boise River to the north. Very likely, also, the lava-flows 

 which obstructed the river a few miles above Boise City turned 

 its course to the southward, so that it may have wandered for 

 some time over the plain in the vicinity of Nampa. 



From the erosion of the Boise" River since the outflow of lava 

 it would seem that the time which has elapsed since the volcanic 

 outbursts is closely comparable with that which has passed since 

 the outflow of the lava forming the Table Mountain in Calaveras 

 and Tuolumne Counties, California, under which the famous 

 Calaveras skull was found some years ago. Furthermore, the 

 occurrence of late Pliocene fossils underneath the lava in western 

 Idaho shows that the lava at Nampa is certainly post-Tertiary, so 

 that this discovery of human relics may properly be synchronized 

 with those under Table Mountain in California. 



In a visit to Sonora, California, and to Bald Mountain, where 

 the Calaveras skull was discovered, I was so fortunate also myself 

 as to run upon evidence of a previously unreported instance of 

 the discovery of a stone mortar under Table Mountain. The mor- 

 tar was found in October, 1887, by Mr. C. McTarnahan, the assist- 

 ant surveyor of Tuolumne County. It was lying in the gravel 

 reached by the Empire Tunnel, and about a mile west of the Val- 

 entine shaft where Dr. Snell found a similar relic. This tunnel 

 had been excavated seven hundred and fifty-eight feet before 

 reaching the gravel, and the mortar was found one hundred and 

 seventy-five feet in a horizontal line from the edge of the Table 

 Mountain basalt, and about one hundred feet below the surface. 

 The object was taken out and laid beside the mouth of the tun- 

 nel, and was given to Mrs. M. J. Darwin, of Santa Rosa, Cali- 

 fornia, who has since given it to me. The mortar is made from 

 a small bowlder of some eruptive rock, and is six and a half 

 inches through ; the hollow being about three and a half inches 

 in diameter, and about three inches deep. 



At the annual meeting of the Geological Society of America, 

 in January, 1891, a similar mortar was reported by Mr. George F. 

 Becker, of the United States Geological Survey, as found under 

 Table Mountain, about five miles south of the Empire mine, near 

 Rawhide Gulch. Mr. J. H. Neale, a well-known mining superin- 

 tendent, made his affidavit that he took this with some other ob- 

 jects of human manufacture from undisturbed gravel underneath 



