324 I. Bowman — Atlantic Preglacial Deposits. 



found in the lower Eocene, and they are accordingly desig- 

 nated as lower Eocene. The fossils are found in ferruginous 

 concretions, reassorted and deposited in their present position 

 as glacial drift. They have apparently been moved- from the 

 north, probably from the sea bottom, and raise the question as 

 to their relation to the Third Cliff deposits. Their relation 

 is, of course, obscure at present, although future dredgings 

 and soundings may throw some light on the subject. 



As has been noted before (p. 321) fossil evidence is almost 

 wanting. The sponge spicules, as already noted, were not 

 identifiable with any degree of certainty. Their value even 

 when identifiable is rarely great. The impression of a single 

 bivalve was noted in the red sands, but as only the rounded 

 and partly obliterated outline was visible it also proved of no 

 value. Fortunately the green glauconitic sands in the upper 

 part of the preglacial series are lignitic and a number of 

 excellent specimens of pyrrotized lignite were obtained. 

 These were carefully examined for me by Dr. E. C. Jeffrey, 

 of the Harvard Botanical Laboratory, to whom I am greatly 

 indebted for a statement of his conclusions, based on extensive 

 comparative studies of lignites from Martha's Yineyard, 

 Staten Island, and Germany. Dr. Jeffrey states :* 



" The lignites from the cliffs at Scituate .... belong to 

 an ancient type of Pityoxylon, earlier than that found in con- 

 nection with the Baltic (Oligocene) amber. They closely 

 resemble, although are not identical with, Pityoxylon from 

 the Cretaceous beds of Staten Island and Martha's Vineyard, 



and are of the same general antique type all of the 



material belongs to one species . . . ." 



The fact that but one species was identified makes correla- 

 tion based on the above determinations quite insecure. From 

 the paleontologic evidence the deposits might be placed any- 

 where between the lower Cretaceous and the Pliocene with 

 probabilities pointing to Eocene or Oligocene. On .the other 

 hand, the lithologic and stratigraphic evidence coupled with 

 the geographic position of the deposits with respect to the 

 Marshfield greensands points to their Miocene age. 



In general, plant remains are known to have a low value as 

 time markers in the geological column, especially such low 

 forms as Pityoxylon f and allied species. The presence of the 

 former is therefore to be considered not as confirmatory but 

 as presumptive evidence which does no violence to the conclu- 

 sions based on stratigraphic grounds. 



Conclusion. 



The conclusions reached after an examination of the fore- 

 going evidence may be stated as follows : 



* Personal letter, March 5, 1906. 

 See Palaeophytologie, Schimper and Schenck, p. 874. 



