50 



those streams : sometimes more : hut as we recede 

 from tlio-e streams, in a south west or west direction, 

 the pebble* invariably grow smaller, so that at the dis- 

 tance of three and four miles west of the streams and 

 particularly GwinnVFalls, they are not bigger, in 

 general, than filberts or walnuts, and from that down 

 to a bird shot, showing that the stream or current had 

 the power of conveying the small pebbles a great dis- 

 tance ; while the larger ones were deposited, soon af- 

 ter they were raised from the bottom of those rivers 

 where, during preceding ages, they had been mostly 

 formed, on or near the margin of those streams. 



It may be a question with some ; from whence came 

 these pebbles ? This seems to be, by no means, a 

 difficult matter to solve. These streams have their 



ground, covered with masses of rocks and rolled stones of various 

 sizes, mostly of a quartzose kind, or in other words of granular 

 quartz. Among these, I discovered in February (1820) rolled 

 masses of Amygdaloid, and of hornblend porphyry, containing; epi- 

 dote, both peculiar to the Blue Ridge or South Mountains in 

 Maryland and Pennsylvania, and which cannot be found in any 

 place, perhaps, within sixty miles of Washington city. More- 

 over, among these rocks were some of a granular quartz, that 

 would weigh, probably, from two to five hundred weight, contain- 

 ing perfect impressions of shells resembling the Terrebratu- 

 lite. This kind of rock, with like impressions, is not, I am credi- 

 bly informed, to be found in any place, in a northern direction, 

 short of Herkimer county state of New-York ; or far beyond the 

 North Mountains in Pennsylvania. From the place at which they 

 now lie, (which is alluvial, and three quarters of a mile from the 

 Potomac r'wr,) to the Atlantic ocean which is about two hundred 

 miles, every mcii of country is of an alluvial formation. 



