27 



of Experimental Geology, Harvard University, through 

 T. A. Jaggar, Jr., the maker and deviser of the studies. 



a. Diagrams showing compression chest w^ith which experi- 

 ments were made. 



b. Four diagrams illustrating influence of rate of compres- 

 sion of models E, F, G. 



c. Three models illustrating the influence of initial varia- 

 tions ; B, C and D. 



Glacial Delta Studies. 



a. Three mounted diagrams showing stages of experiment. 



b. One unmounted diagram showing cross section of delta. 



c. One unmounted diagram showing special study of water 

 level in relation to formation of delta. 



Ripple Mark Studies. 



a. Four plates showing influence of amplitude by oscillation. 



b. One plate showing cross ripples. 



Sand-blasted Pebbles. 



a. Limestone pebble, engraved and polished by the drifting 

 sand of the desert, Wadi Amara, Arabia Petrea. 



b. Pebble of snowy gypsum, with similarly engraved sur- 

 face, Wadi Amara, Arabia Petrea. 



The above were collected by Dr. Bolton. They may 

 be compared with Exhibit ic. Exhibited by Dr. A. A. 

 Julien, Columbia University, and H. Carrington Bolton, 

 Washington, D. C. 

 A Series of Copper Ores and Wall-rocks, from Butte, 

 Mont., collected June, 1896, by J. F. Kemp, by whom 

 they are exhibited. The ores are chalcocite, enargite, 

 bornite, chalcopyrite and tetrahedrite and all contain sil- 

 ver. Rhyolite is an important rock in the neighbor- 

 hood of the veins, and light-colored granite is not far 

 away. Silver mines also occur in the camp, with an en- 

 tirely different set of minerals from the copper. A few 

 of these are shown, with their gangue of rhodochrosite. 

 The specimens illustrate also the quartz ledges that con- 

 stitute the outcrops of the veins. 



