278 PROCEEDINGS OF THE CALIFORNIA 



to disappear by evaporation, as the concretionary deposits, to which I last year 

 called the attention of the Acadt-my, are found at an elevation of two hundred 

 feet above the level of the valley, and they could only have been depo-ited as 

 the water became concentrated by evaporation. I am of opinion thai Queen's 

 River Valley, and a large extent of country to the south and west of it, formed 

 part of a secondary basin, in which water to the depth of three or four hundred 

 feet must have disappeared by evaporation. Over the whole of the area of this 

 secondary basin, as far as I have visited it, unmistakeable evidences are seen of 

 the gradual evaporation of a large body of water. Not only are the rocks and 

 boulders surrounded by a thick coating of concretionary matter, but every solid 

 body that was beneath the surface of the water seems to have aft'orded a nucleus 

 for its deposition. Large numbers of Aaadonta shells are found on the surface 

 of the ground, entirely encased in this concretionary substance to the thickness 

 of two or three inches. I propose, however, in a subsequent paper, to describe 

 more fully the structure and composition of these deposits. The eastern edge of 

 this secondary basin is formed by the Santa Rosa mountains. On the north is 

 the high land between the Vicksburg and Santa Rosa ranges, and the low 

 divide between Divide and Puebla valleys. Directly south of the Bottle 

 Creek raiige the basin is separated from the valley of the Humboldt by a low 

 range of hills about fifteen miles north of the latter river. As to its extent 

 farther to the westward, I have no data. It certainly includes the Black Rock 

 Desert, and I think a considerable extent of country still more to the South and 

 West. 



Professor Davidson said that having been asked to solve a ques- 

 tion in the subdivision of a circular ring into two or more circular 

 rings of equal area with each other, he had found a general formula 

 "which governed that and some other problems suggested by it, and 

 which are believed to be new. These he stated in the following 

 order : 



I. Given the diameter of a circle, to determine, in terms of 

 that diameter, the consecutive diameters of the interior circles 

 which will divide it into circular rings and a central circle, of equal 

 values with each other. 



To divide it into n circular rings and a central circle, call d the 

 given diameter; x^ ?/, etc., the diameters next interior, and (^w-V) 

 and iv^ the last two diameters ; then, 



etc. 



II. Given the two diameters of a circular ring, to determine, 



