GEOLOGIC EXHIBITS IN THE NATIONAL 

 ZOOLOGICAL PARK 



By R. S. Bassler 

 Head Curator, Department of Geology, U. S. National Museum 



[With 8 plates] 

 INTRODUCTION 



Geologic features illustrated by exhibits in the several buildings of 

 the United States National Museum and the Department of the In- 

 terior are well known to Washington visitors, but few are aware 

 of the many out-of-doors rock displays in the vicinity of the Nation's 

 Capital, especially those in the Zoological Park under the supervision 

 of the Smithsonian Institution. In a previous article, "A Geologist's 

 Paradise," ^ the general geology of Washington and its environs was 

 discussed, but that part of Rock Creek Park occupied by the Zoo 

 offers so many special points of geologic interest as to make this 

 comparatively small area worthy of a more detailed description. 

 The exhibits here are in almost all cases natural outcrops,^ which, 

 however, in some instances have been better exposed by man or pro- 

 tected against destruction. 



A large part of Rock Creek Park is occupied by a typical V-shaped 

 stream valley cut in the low plateau upon which the higher north- 

 western part of Washington is built. Here, the greatly folded hard 

 rocks representing the oldest recognizable periods of earth history 

 are well exposed by stream erosion^ but the whole region, formerly 

 the site of high mountains, the older Appalachians, as indicated by 

 the tilted strata, has been so completely planed off during the course 

 of geologic time that it is a plain surface, although elevated now- 

 about 400 feet above sea level. This is the Piedmont Plateau^ so 

 called because of its position at the foot of the Blue Ridge Moun- 

 tains to the west. Like the Blue Ridge, the Piedmont is an example 

 of the physiographic provinces^ the large natural geographic divisions 

 of our country that result from their geologic structure and the 



1 Smithsonian Ann. Rep. for 1933, pp. 327-332, 1935. 



■ The italicized words throughout this sketch call attention to the various geologic 

 features illustrated near the entrances or within the Zoo Park. An alphabetical list 

 of these Items closes this article. 



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