PREFACE TO THE SECOND EDITION. 



xvii 



duced by me, and much more, in an article which appeared 

 in The Popular Science Monthly four years before the pub- 





M: 



lication of the volume (November, 1888). In this article 

 he had said : 



" But it is in the aqueo-glacial gravels of the Delaware 

 River at Trenton, which were laid down contemporane- 



