Feather slonhaugh'^s Geological Report. 



97 



power of water to deepen its own beds, than the singular area 

 I have mentioned, as well as the falls themselves, which are 

 amongst the most picturesque localities of this country.* 



A little further to the westward, the slaty rocks again dip 

 to the eastward, and are occasionally almost vertical, become 

 contorted, and vary in color. At Seneca creek the soil begins 

 to be reddish, and on the west side a soft red sandstone comes 

 in, the beds of which appear horizontal from the canal, but 

 upon examination have a regular anticlinal structure. Seams 

 of loose red shale abound between the strata of sandstone ; 

 specimens also of anthracite coal have been obtained from this 

 neighborhood, the nature of which not having been well ap- 

 prehended, has induced some persons to suppose that this 

 locality might be a continuity of the Chesterfield coal field of 

 Virginia. It deserves a remark that the red shale is a con- 

 stant concomitant of the anthracite coal of the Alleghany sys- 

 tem. A few miles from Seneca creek, and 24 miles by the 

 canal from Georgetown, the strata dip again to the westward. 

 At Mr. Lee's quarry, from whence valuable slabs are obtained 

 for the public works at Washington, fine casts of calamites, 

 with impressions of other plants, are found. Seams of red 

 shale separate the beds of sandstone occasionally ; carbonate 

 of copper is frequent, and small veins of anthracite coal. The 

 country for the next fourteen miles presents fine slopes and 

 levels, and is occupied for agricultural purposes, when an anti- 

 clinal ridge of soft red shale comes in upon the river at right 

 angles, dipping to the southeast. About five miles before 



* The nature of the power of the water in this locaUty in ancient times, before 

 the bed of the river was contracted, will be better understood by stating that the 

 falls are nearly at the head of a natural inclined plane, measuring, by the bends of 

 the river, upwards of 11 miles to Georgetown, and having a fall of 168 feet to the 

 tide- water level. This gives an average of 14§ feet per mile, a force which, added 

 to the immense period it operated upon these rocks, probably ever since the eleva- 

 tion of the Atlantic primary chain, sufficiently adequate for the phenomena now 

 presented in the bed of the river. In the succeeding inclined plane of 8f miles, 

 the fall is only 32 feet. 



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