31 



19- A Series of Maps Illustrating the Recent Progress 

 of the United States Geological Survey in impor- 

 tant districts, viz : 



a. Yellowstone Park, showing the areal geology. 



b. A portion of Eastern Tennessee, covering six atlas sheets, 

 giving the distribution of the Paleozoic rocks. 



c. A portion of Virginia and West Virginia, comprising 

 three atlas sheets, also giving the distribution of Paleo- 

 zoic rock. 



d. Three sheets of a folio in Virginia, giving specially the 

 distribution of the Carboniferous coal-bearing rocks, the 

 economic features and the structure of the region. 



e. A portion of the Gold Belt region of California, cover- 

 ing two atlas sheets, showing the rocks of the Gold Belt 

 and also an old volcanic cone in the Sacramento Valley. 



Exhibited by the United States Geological Survey, 

 through Mr. Bailey Willis, Geologist and Assistant to 

 the Director. 



Several topographical sheets are added by the Chair- 

 man of the Section, which illustrate the maps that can 

 be procured, so far as made, for five cents each, postpaid, 

 on application with remittance to the Director of the 

 United States Geological Survey, Washington, D. C. 



3o. Brecciated Dikes from the Lake Champlain Valley. 



Exhibited by Theodore G. White, Columbia Uni- 

 versity. 



Three instances of diabase dikes, thickly packed with 

 partially rovmded fragments of granite, gabbro, labra- 

 dorite, hypersthene, sandstone, etc. 



a. From Cumberland Head, near Plattsburgh, N. Y. ; a 

 dike I ^ feet wide, cutting an anticline of the Trenton 

 limestone, as shown in the accompanying photograph. 

 The amygdaloidal edges of the dike are also shown. 



b. From the end of Willsboro' Point, N. Y. ; a dike 6 feet 

 wide in the Utica slate. 



