626 ANNUAX, REPORT SMITHSONIAN INSTITUTION, 19 3 



moist and warm conditions. In rock weathering, " hydration is an 

 important factor, the amount of water increasing rapidly as decom- 

 position advances. In the earlier stages of degeneration it is doubt- 

 less the most important factor. There is, moreover, among the 

 siliceous crystalline rocks, in every case a loss in silica, a greater pro- 

 portional loss in lime, magnesia, and the alkalies, and a proportional 

 increase in the amounts of alumina and sometimes of iron oxides, 

 though the apparent gain may, in some cases, be due to the change 

 in condition from ferrous to ferric oxide. As a whole, however, 

 there is a very decided loss of materials. Among siliceous crystal- 

 line rocks, this loss, so far as shown by available analyses and calcu- 

 lations, rarely amounts to more than CO per cent of the entire rock 

 mass. Among calcareous rocks, on the other hand, it may, in 

 extreme cases, amount to even 99 per cent." (1906a : 220.) 



About Washington, Merrill had observed granitic rocks " so disin- 

 tegrated at a depth of 80 feet from the present surface as to be read- 

 ily removed by pick and shovel." About Atlanta, Ga., " the rocks 

 are ' completely rotted ' to a depth of 95 feet, while ' incipient decay ' 

 may reach to a depth of 300 feet." (1906a: 271.) 



When F. P. Dewey in 1889 resigned his curatorship of economic 

 geology in the National Museum, Merrill was asked to take over 

 this work also. The task of overhauling and installing the nonmetal- 

 lic economic collections early focussed his attention on these sub- 

 stances, resulting not only in a greatly improved exhibition collec- 

 tion but as well in a book. Guide to the Study of the Collections in 

 the Section of Applied Geology: Nonmetallic Minerals. (1901c.) 

 The popular demand for this shortly exceeded the supply and it was 

 republished in modified form by John Wiley & Sons as The Non- 

 metallic Minerals. The purpose of this book is " to bring together 

 the widely scattered notes and references relative to the occurrences 

 and uses of sundry minerals of value other than as ores of metals." 

 (1910b: iii.) 



MERRHiL AS PIONEER IN THE APPLICATION OF PETROLOGY TO THE STUDY 



OF METEORITES 



No geological problem interested Merrill more than that of meteor- 

 ites, and of his entire bibliography of about 200 titles, no fewer than 

 80 have to do with these most interesting celestial bodies. The first 

 three papers appeared in 1888 and the last one after his death, while 

 the 20 years of greatest activity began with 1907. 



Previous to 1897 the meteorites in the National Museum were con- 

 sidered as belonging to the mineralogical department, but in that 

 year they were transferred to the division of geology and " recog- 



