J, E. Burbank — Microseisms Caused by Frost Action. 475 



tinuous as long as the ground is frozen and continue without 

 appreciable diminution when the frozen ground is covered 

 with a blanket of snow. When the ground is covered with 

 snow the microseisms are due to the thawing out of the lower 

 layers of frozen ground in contact with the warmer layers 

 below. 



Attention was especially directed to those cases of cold 

 waves with freezing temperatures approaching Cheltenham 

 and in no case could any microseisms be detected until the 

 ground at Cheltenham had begun to freeze. 



The above evidence does not disprove a relation between 

 microseisms and frost action at a distance, but it places a limit 

 on the magnitude of such action. 



Cheltenham, Md., August, 1911. 



Art. XLI. — Dahllile (Podolite) from Tonopah, Nevada ; 

 Vodckerite, a New Basic Calcium Phosphate / Remarks 

 on the Chemical Composition of Apatite and Phosphate 

 Rock ; by Austin F. Rogers ; with Analyses by G. E. 



POSTMA. 



My attention was directed to a chemical study of apatite 

 and related minerals by the recognition of a calcium carbono- 

 phosphate on a mineral specimen from Tonopah, Nevada, 

 kindly sent to me by Mr. S. C. Herold, a mining engineer. 

 This specimen, which is from the Mizpah mine of the Tonopah 

 Mining Company, consists of iodyrite, hyalite, quartz, man- 

 ganese dioxide, and a white drusy coating of minute hexagonal 

 crystals. As these hexagonal crystals seemed to effervesce in 

 acid, they were provisionally referred to calcite. Optical tests 

 failed to confirm this determination, for the fragments had 

 weak, instead of strong, double refraction. The weak double 

 refraction suggested apatite. As a good phosphate test was 

 obtained, the mineral naturally was called apatite and the effer- 

 vescence was attributed to an error in observation. 



On reading a paper* on the probable identity of dahllite with 

 podolite, it occurred to me that the Tonopah mineral might 

 belong to one of these carbono-phosphates, so the solubility 

 test was tried again very carefully. There was distinct effer- 

 vescence with warm nitric acid. Observed under the micro- 

 scope, the bubbles come from the hexagonal crystals and from 



* Schaller, this Journal, vol. xxx, 309, 1910. 



