REPORT ON THE DEPARTMENT OF LITHOLOGY AND PHYSICAL GEOLOGY 

 IN THE U. S. NATIONAL MUSEUM, 1887. 



By George P. Merrill, Curator. 



The work of the year has been almost wholly in the line of preparing 

 the ^exhibition and reserve series, and this necessitated the study 

 with the microscope of a large number of thin sections of rocks. To 

 facilitate this work the curator has passed three days of each week from 

 December until March in the petrographical laboratory of the Johns 

 Hopkins University at Baltimore. While there, several hundred slides 

 were examined, and from the results obtained I have been enabled to 

 classify and arrange a considerable amount of material which has been 

 accumulating for many years, but which could not be utilized owing to 

 a lack of proper identification. 



No systematic collecting has been carried on during the year. In the 

 course of a six weeks' outing in Montana during August and Septem- 

 ber, in company with Dr. A. C. Peale, of the U. S. Geological Survey, I 

 obtained much material of interest and value, which will be noticed 

 under the head of accessions. During a hurried trip to California in 

 March I also obtained some valuable material and made arrangements 

 for a series of exchanges by which I hope to gain much of interest. 



Four new cases for the accommodation of relief maps have been con- 

 structed from designs furnished by myself, and have proved very satis- 

 factory. In one instance the map — that of the Comstock Lode and 

 Washoe district, Nevada, from surveys by Becker — is arranged to lie 

 horizontally and is protected by a covering of plate- glass and a mahog- 

 any railing. In the other three instances the maps are inclined at a high 

 angle, the bottoms being some 1 8 inches from the floor, and each case 

 carrying two maps, one on each side. The cases are so constructed that 

 when desired they can be separated vertically into two parts, each half 

 constituting a case by itself. This arrangement is of especial conve- 

 nience whenever it is desired to remove temporarily oue or more of the 

 maps to the lecture- room. A large wall case, consisting of three inde- 

 pendent sections, has also been constructed for the west end of the ex- 

 hibition hall. Owing to the two large doorways, gas-meter, and hose- 

 pipe, no perfectly satisfactory case for purposes of exhibition could be 



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