2 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 60 



The writer began an examination of the sands from Idaho pre- 

 served in the United States National Museum as part of the work of 

 preparation of a lengthy manuscript on the minerals of that State. 

 While of absorbing interest, the work proved to be tedious, and the 

 lirait to the amount of data obtainable from the study of the 

 sands is prescribed by the amount of time available for their investi- 

 gation. A single gram of the material may contain hundreds or 

 even thousands of crystals which can not all be thoroughly examined 

 in several days of steady work. The results obtained are not as com- 

 plete or as conclusive as might be wished, but even thus they seem to 

 indicate that some previous investigators have made errors in their 

 identifications of some of the minerals. Under the circumstances 

 this is far from surprising. Identifications must rest almost entirely 

 upon the recognition of visible characters under the microscope and 

 an ordinary monocular microscope is unsatisfactory for this purpose 

 because of its limited field of vision and lack of focal depth. Chemi- 

 cal examinations of the aggregated minerals of a sand of mixed char- 

 acter are obviously little better than worthless and no single grain 

 which may be selected has sufficient substance usually to yield dis- 

 tinctly visible qualitative or measurable quantitative chemical re- 

 actions. The modern methods of optical research by the use of im- 

 mersion media of known refractive index, which are so indispensable 

 in the study of fine-grained mineral aggregates are almost inappli- 

 cable in the study of these sands. This is due to the fact that nearly 

 all of the minerals of interest are either opaque or have such exceed- 

 ingly high indices of refraction as to fall well above the range of 

 the series of stable immersion media available to any but a few 

 specialists in optical mineralogy. In the present investigation the 

 writer used a highly improved modern binocular microscope of the 

 type recently manufactured by the Spencer Lens Company, of 

 Buffalo, N. Y. This instrument presents a broad field with a splen- 

 did depth and sharpness of focus and it is possible to work in the 

 field selecting individual grains and crystals with a wax tipped wire 

 or a pair of forceps. Crystals were mounted in approximately ver- 

 tical position on the wire and it was then the work of but a short 

 time to orient them correctly for measurement on a Goldschmidt 

 two-circle goniometer. The identity of some crystals was not even 

 suspected until the angles measured had been carefully plotted and 

 the symmetry thoroughly worked out. 



The scheme of examination adopted, aside from the use of the 

 goniometer, is relatively simple. The sands should be concentrated 

 as far as possible by panning, or some other simple means of gravity 

 concentration, thus eliminating the uninteresting lighter materials, 

 as quartz, fragments of feldspar, micas, chlorite, etc. The remain- 

 ing heavy concentrate should be carefully dried and then worked 



