1884.] NEW YORK ACADEMY OF SCIENCES. 33 



before alluded to, enable us, in the writer's opinion, to leave 

 these out of consideration in the discussion. 



(2) The fossiliferous pebbles have evidently been silicious 

 limestone. There are no such rocks now outcropping in prox- 

 imity to the Pre-glacial Drift formation, and they nnist either 

 have come from the Palaeozoic regions northwest of the Kitta- 

 tinny Mountains, or from rocks now covered by the Cretaceous 

 and newer formations. This is a question on which we are not 

 likely to obtain any conclusive evidence without a great deal of 

 detailed held observation, 



(3) There are gravel beds of considerable thickness interbedded 

 with the Cretaceous clays. Mr. Merrill reported last Monday 

 evening a section at Glen Cove, Long Island, seventy- three feet 

 high of interstratified clay and gravel. At Fish House Sta- 

 tion, N. J., a few miles above Trenton, the gravel was four 

 feet thick in one of the clay pits when visited in 1883, and in 

 this gravel I found a pebble containing a broken cast of A t/'ypa 

 reticularis. A gravel-bed was encountered in a well bored at 

 Sayreville, N. J., and it has been noticed in smaller amounts 

 elsewhere. Sand-beds are everywhere interstratified with 

 those of clay. It is a safe assumption, I believe, that the 

 origin of these Cretaceous gravels and sands was closely 

 related to, and certainly contemporaneous with the deposition of 

 the clays. The clays are generally believed to be the result of 

 kaolination of the feldspars of crystalline rocks ; everything 

 points to the truth of this hypothesis, and indeed at Trenton 

 the process may actually be seen in progress. 



(4) The amount of erosion since the deposition of the clays 

 has been very great, and while not accurately determinable, 

 must have amounted to several hundreds of feet, if the indica- 

 tions found in the structure of the Navesink Highlands and 

 other hills are to be relied on. 



Finally, considering the facts above cited, it appears to the 

 writer that a considerable amount, if not the greater part of 

 the Pre-glacial Drift, may well have (;ome from the erosion of 

 Cretaceous gravel-beds. That these are the more resistant por- 

 tions of disintegrated crystalline rocks is quite clearly shown. 

 But the place of origin of the fossiliferous pebbles remains a 

 mystery, and, it may be added, little more is known of the 

 origin of the saccharoidal quartzite masses. 



/ 



