1898.] NATURAL SCIENCES OF PHILADELPHIA. 97 



fluid lavas of the Mesozoic era, it is only a question of time when 

 this one also will have been disrupted and obliterated like its an- 

 cient colleagues of the vicinity. 



Ancient craters necessarily decay and crumble away just as any 

 other exposure of rock will do. It is well-known to those versed in 

 the special literature of the subject, that collapsed craters have been 

 found and recognized in Europe, and it might reasonably be ex- 

 pected that in time the discovery of similar phenomena existing here 

 would result from careful observation. 



In the literature of the Second Geological Survey of Pennsylva- 

 nia nothing is mentioned of the Pottstown Hill, except that Trap 

 occurs there. But that an entire crater of Mesozoic age is still in- 

 tact at that spot nobody seems to have even guessed ; at least no 

 geologist appears to have looked at it, much less to have explored 

 or described it. That the deep cauldron is an ancient crater, I am 

 fully convinced. 



