Penjyhaniaj Philadelphia, 123 



and the ftone afford either a fine or a coarfe 

 fand, which is wafhed away by the water 

 when in fpring, or at other times it is 

 high enough to throw its waves into the 

 cavity. This was the opinion of Mr. 

 Bartram about the origin of thefe cavities. 

 The Royal Society of Sciences at London, 

 has given a favourable reception to, and ap- 

 proved of them.* The remarks which I 

 made in the fummer of the year 1743, 

 during my ftay zt Land^s-Ortt in my coun- 

 try, will prove that I was at that time of 

 the fame opinion, in regard to thefe holes. 

 I have fince further explained this opinion 

 in a letter to the Royal Academy of Scien- 

 ces ', and this letter is ftill preferved in the 

 Academy's Memoirs, which have not yet 

 been publifhed. But there is great reafon 

 to doubt, whether all cavities of this kind 

 in mountains, have the fame origin. 



Here are different fpecies oi Mulberry 

 trees, which grow wild in the forefls of 

 north and fouth America. In thefe parts 

 the red mulberry trees are more plentiful 

 than any other. However Mr. Bartram 

 alfured me that he had likewife feen the 



white 



• How far this approbation of the Royal Society, ought 

 to be credited, is to be underftood from the advertifements 

 publiftied at the head of each new volume of the Philofophi- 

 cal Tranfadions. F. 



