GEOLOGY IN NATIONAL MUSEUM MERRILL. 267 



life. This clay represents the mud which was deposited on the sea 

 bottom, while the limestone layers resulted from the cementation 

 by calcareous matter of the remains of animal life. 



Explanatory labels of this as well as most of the other large ex- 

 hibits of this nature, bear photographs showing the original posi- 

 tion of the specimens as exposed in the field. 



Stratigraphic series. — The stratigraphic series in the long contin- 

 uous case against the north wall (see right-hand side, pi. 2, fig. 1) is 

 especially adapted for the serious student of geology. It contains 

 in the sloping portion selected series of characteristic fossils of each 

 of the geologic formations, while above in the upright part is a cor- 

 responding series of hand samples of the typical rocks. Explanatory 

 labels are numerous, while photographs of type areas of outcrop 

 and maps showing the distribution of the various formations are 

 included, giving the student here in small compass as much infor- 

 mation on each formation as is possible under the conditions. 



Structure section across continent. — Of equal or greater interest 

 is the painted geological section 90 feet long above the upright case 

 extending the entire length of the hall. This represents the sedi- 

 mentary and igneous rocks exposed on the surface along an east- 

 west line across the United States. The section does not follow a 

 straight line across the continent being drawn through those areas 

 where the greatest amount of geological data is available. 



Beginning at the Pacific Ocean, the line crosses the San Francisco 

 peninsula and continues diagonally northeastward to the Sacra- 

 mento Valley. This portion is based on a manuscript section made 

 by Prof. A. C. Lawson, of the University of California. From the 

 Great Valley to the southwest corner of Nevada the work of the 

 U. S. Geological Survey has furnished the data. Here connection is 

 made with the work of the survey of the Fortieth Parallel, whose 

 sections through Nevada, Utah, and Wyoming are utilized. From 

 the Wasatch Range the line runs north of the Uintah Moutains 

 to a point north of Leidy's Peak. Here there is a change in direc- 

 tion to the southeast, and the Uintah Range is crossed diagonally, 

 the line being carried across the Green River Canyon at Split 

 Mountain and the western end of the Yampah Plateau. From this 

 point to the Elk Mountains in Colorado the section is based on the 

 work of the Hayden Survey. In the Elk Mountains the United 

 States Geological Survey quadrangles were utilized. From the Elk 

 Mountains to Pike's Peak and eastward in Colorado, the work of 

 the Hayden Survey is again the source of the data. From Pike's 

 Peak eastward to St. Louis the line is practically straight, and in 

 Kansas and Missouri it is based on the work of the geological sur- 

 veys of those States. From St. Louis the line is again deflected to 

 the southeast, so as to make connection with the work of the U. S. 



