1. Bowman — Atlantic Preglacial Deposits. 325 



(1) The lower part of the Third Cliff section is preglacial. 

 This is based on the character of the deposits, the entire 

 absence of erratic material, and the relation and sequence of 

 the unconformities. The suggestion that these beds may be 

 interglacial is opposed by a number of facts which point to the 

 improbability of this occurrence. In the first place, two marked 

 unconformities such as occur within the lower deposits, to- 

 gether with the individual character of the different beds, indi- 

 cate a distinct even if small change in the conditions of 

 deposition which one would expect should be marked elsewhere 

 by deposits of a similar nature. JN"o interglacial deposits of 

 this character are known on the Atlantic coast. It would be 

 singular, though not impossible, that an interglacial deposit of 

 this thickness should elsewhere be swept away, a single rem- 

 nant preserved in this locality only. It is more reasonable that 

 extensive Cretaceous and Tertiary terranes should be removed 

 leaving here and at Marshfield and Gay Head remnants of a 

 similar nature. It would be very peculiar indeed if an inter- 

 glacial deposit were to simulate so closely the stratigraphic suc- 

 cession and lithologic qualities of beds of known Cretaceous 

 and Tertiary age, and at the same time be the sole representa- 

 tives of their kind on the coast. To this fact we may add that 

 the oldest known bowlder bed in New England is present here 

 (seep. 317) and that it occurs above the unconformity represen- 

 ted at C, tig. 1, that is to say, above the most marked uncon- 

 formity of the whole section and one which represents the most 

 profound break in the conditions of deposition. 



(2) The occurrence of Cretaceous and Tertiary deposits at 

 Martha's Yineyard, 50 miles south of Third Cliff, and of Ter- 

 tiary deposits at Marshfield, seven miles south of Third Cliff, 

 make it seem not unlikely that deposits of the same age once 

 extended farther north, as well as farther inland, though sub- 

 sequent erosion may have all but completed the removal of 

 such deposits. 



(3) The similarity of the material and the many points of 

 similarity of sequence in these several places indicate the strong 

 possibility that the Third Cliff beds are to be correlated with 

 those farther south. 



(4) The identity of plant remains offers the same possibility 

 based on an independent line of evidence. 



(5) The convergence of independent possibilities renders the 

 following more than possibilities: they may be accepted as 

 probabilities : 



(a) The underlying yellow clay and the yellow and white 

 sands are considered as probably upper Cretaceous, (b) The 

 overlying dark sands and clays are probably Miocene though 

 possibly Eocene or Oligocene. 



