REPORT OF DEPARTMENT OF PHYSICAL GEOLOGY. 233 



specimens, each of which is accompanied by a printed label stating: ta 

 which of the three principal groups it belongs, what type of structure 

 it represents, and also the name of the rock specimen itself, the localitj- 

 from whence it came, and the name of the donor or collector. 



In preparing the collection of rock-forming minerals, rocks have been 

 regarded as sim]»ly mineral aggregates of more or less complexity of 

 structure and composition. The collection, therefore, includes repre- 

 sentative specimens of all those minerals which commonly form an ap- 

 preciable part of large rock masses, the rarer minerals and the gems 

 being excluded. Each mineral species is shown in its several varieties, 

 and is accompanied by a printed label giving its crystalline system, 

 chemical composition, and the sjiecies of rock or rocks in which it com- 

 monly occurs. If the mineral itself possesses any economic value, this 

 is also stated. This collection at present comprises 150 specimens, rep- 

 resenting in their different varieties 46 mineral species. 



The building-stone collection comprises only such material as is used 

 in the rough or finished state for some form of building or ornamental 

 work. All the stones of this collection are designed for exhibition, and 

 for this purpose are cut into -l-inch cubes and finished in the following 

 manner: Polished or fine-sanded in front; drafted and pointed on the 

 left side ; drafted rock face upon the right side ; rock face behind, and 

 smooth sanded or chiseled upon the top and bottom. Each block, when 

 finished, has its catalogue number painted upon it, and is put on exhibi- 

 tion, accompanied by a printed label giving the scientific name of the 

 stone, its geological age, color, texture, &c., together with the location 

 from which it was taken, the names of the quarry-owners or lessees, 

 and that of the donor or collector; the purpose being to so arrange and 

 label the entire collection that all interested can, within the space of a 

 few hours, see and examine for themselves all the varieties of building^ 

 stone quarried in the United States, together with very many from for- 

 eign localities. 



As a supplement to the building-stone collection, to illustrate the 

 adaptability of certain kinds of stone to architectural purposes, a series 

 of photographic negatives of some of the more important stone build- 

 ings of the country has been obtained, from which enlarged prints (30 

 by 40 inches) have been prepared. These prints have been painted in 

 a manner to represent the natural color of the stone of which the build- 

 ings are constructed. The series comprises ten photographs of buildings 

 constructed of the following materials: One each of granite, gneiss, 

 limestone, marble, and serpentine, and five of sandstone, or sandstone 

 in connection with brick. 



Physical geology. — The collections of the department that may be ap- 

 propriately grouped under the head of i)hysical geology, that is, as of 

 greater interest from bearing the marks of physical agencies than from 

 their lithological characters, are at present comparatively limited. The 

 more important of these are the collection of lavas from Ice Springs 



