NO. 2 SMITHSONIAN EXPLORATIONS, I918 21 



primarily to such agricultural and other colleges as give instruction 

 in rock weathering and soil formation. A series of from two to four 

 specimens was obtained from each of the seven varieties of rocks 

 showing the fresh and intermediate steps in the present stage of 

 its decomposition. The types selected include granite-gneiss, dia- 

 base, gabbro, soapstone, sandstone, and limestone. The railroad 

 cuts in the vicinity of North Garden and Chatham in Virginia, and 

 Mount Hope and Washington Junction in Maryland, afforded, 

 respectively, the granite-gneiss, diabase, gabbro, and sandstone, and 

 the quarries at Alberene, Virginia, and Frederick, Maryland, yielded 

 the soapstone and limestone. In every case the oxidation had pro- 

 ceeded sufficiently to result in the formation of reddish- or yellowish- 

 brown soil, but in the case of the North Garden granite-gneiss, per- 

 fectly fresh rock could not be obtained. To supply this deficiency, 

 a series of specimens from the granite-gneiss of the District of 

 Columbia was included, although its weathering had not passed the 

 stage of mechanical disintegration. Despite the fact that such 

 materials do not readily lend themselves to exhibition purposes, 

 several choice residual nodules of gabbro and diabase (so-called 

 nigger heads) one to two feet in diameter were collected for Museum 

 display. 



In order to fill certain gaps in the ore and rock collections. 

 Dr. Martin was also detailed to visit localities in Pennsylvania, New 

 Jersey, and New York, and secure a quantity of material from each. 

 Brandywine Summit, Pennsylvania, yielded some excellent cleavage 

 fragments of orthoclase ; Peekskill, New York, a select grade of 

 emery rock ; North River, New York, hand size pieces of abrasive 

 garnet. From the dikes at Franklin Furnace and Beemersville, New 

 Jersey, was secured a supply of uncommon intrusive rocks, camp- 

 tonite and nepheline-syenite respectively. Both of these formations, 

 as well as the peridotite, associated with the emery and the syenitic 

 country rock of the garnet, were found to have suffered considerably 

 from the action of the weather since glacial times, and appropriate 

 specimens showing this process were collected incidentally for the 

 study series. 



During the field season of 1918, Drs. R. S. Bassler and C. E. Resser 

 of the Division of Paleontology continued the search begun in recent 

 years for large exhibition specimens to illustrate the various phases 

 of structural geology and stratigraphic paleontology. Dr. Bassler 



