DEPARTMENT OF LITHOLOGY AND PHYSICAL GEOLOGY. 201 



(12) Two fine samples of Fulgurite on eruptive rock; gift of Mr. J. S. DiUer, U. 

 S. Geological Survey. 



(13) A large collection of eruptives, metamorphic, and sedimentary rocks from 

 Colorado; received from S. F. Emmons, U. S. Geological Survey. This includes a 

 type collection of the rocks aud ores of Leadville, as described by Messrs. Emmons 

 and Cross in Monograph xii, U. S. Geological Survey. This is by far the most valu- 

 able accession of its kind of the year. 



(14) A fine series of fossil coral for cutting and polishing; received by way of 

 exchange from C. C. Nutting, Iowa College, Iowa. 



(15) A series comprising one hundred photographs. Scenery of United States, 

 New Zealand, and Australia. This is old material received from the Centennial Ex 

 position in 1^76, but not before assorted and catalogued. 



(16) A fine large block (22 by 21 by 15 inches) of Ophite marble from Thurman, 

 Warren county, New York. Gift of E. L. Baxter. This specimen is of interest not 

 merely on account of its unique appearance, but also on account of the light which, 

 it throws on the origin of this class of rocks. 



( 17 ) A complete series of specimens collected at intervals of every 50 feet from the 

 tunnel of the new aqueduct extension in this city. For this collection we are in- 

 debted to Mr. Thomas Robinson, formerly of Eoward University. That the collec- 

 tion was in process of preparation has been noted in my previous report. 



ROUTINE WORK. 



The general character of the routine work of the year may be best 

 inferred by a perusal of the following outline showing the scope of the 

 department. * 



Considering geology not merely as a science treating of the compo- 

 sition and structure of the earth, but as one which comprises its origin 

 and history also, one whose aim it is to " trace the progress of our 

 planet from the beginning of its separate existence through its various 

 stages of growth down to the present condition of things," we begin 

 with a consideration of— 



I. The earth in its cosmical aspect. — In this first primary division the 

 earth is represented as a planet and compared with other members of 

 the solar system. This can of course be done only by means of models 

 aud illustrations of various kinds. 



II. The structure of the earth — Geology. — This second primary division 

 which comprises the science of geology as ordinarily understood, is 

 subdivided into five sections, each of which is capable of further sub- 

 division. Considered in the order adopted, these are : — 



A. Geognosy; a consideration of the materials of the eartWs substance. — 

 Under this section are to be shown (1) the sixteen more common ele- 

 ments which in their various combinations are estimated to form about 

 99 per cent, of the substance of the earth's crust ; (2) the minerals 

 which, resulting from these combinations, go to make up rock masses ; 

 and (3) the rocks themselves. All the substances required for these 

 exhibits are of such nature as to admit of their being readily utilized. 

 Not even the fact that an element is a gas both colorless and tasteless 



* Extracts from a paper on Geological Museums read by the Curator before the 

 Philosophical Society of Washington. 



