I. Bowman — Atlantic Preglacial Deposits. 313 



Art XXIX. — Northward Extension of the Atlantic Pre- 

 glacial Deposits /* by Isaiah Bowman. 



Outline. 

 Introduction. 



Lithologic and Structural Features. 

 Preglacial Series. 



(1) Basal Clays. 



(2) White and Yellow Sands. 



(3) Eed Sands. 



(4) Dark Green Sands and Clays. 

 Glacial Series. 



(1) Stratified Deposits. 



(2) Unstratified Deposits. 



Succession of Events in the Deposition of the Third Cliff Beds. 

 Former Interpretations. 



Occurrence of Preglacial Deposits near Third Cliff. 

 Correlation with similar Deposits farther South. 



Continuity of Deposits. 



Similarity of Materials. 



Paleontologic Evidence. 

 Conclusion. 



Introduction. 



Heavy winter storms on the New England coast following 

 the unusually dry autumn of 1904 resulted in many changes 

 in coastal topography, among which were the rapid cutting 

 back of headlands of soft material and the freshening of 

 cliffs. Good opportunities were thus presented for the study 

 of exposed geological sections. The Third Cliff section near 

 Scituate, Massachusetts, is of special interest because of the 

 lithologic and stratigraphic homologies between the exposed 

 beds and preglacial deposits farther south and their bearing 

 on the question of the northern limit of the Atlantic Cre- 

 taceous and Tertiary. The nearest known outcrop of deposits 

 of Cretaceous age is at Gay Head, Martha's Vineyard, 52 

 miles south of Third Cliff ; the nearest known deposits of 

 Tertiary are the Miocene Greensands at Marshfield, 7 miles 

 south of Third Cliff. The latter are not commonly known to 

 occur though they were noted by Hitchcockf as early as 1841 

 (p. 91), the latest text-book of Geology;); stating that " The 

 northernmost exposure of the Miocene on the Atlantic coast 

 is on Martha's Vineyard." 



Third Cliff is one of a series of four cliffs in close succes- 

 sion twenty miles southeast of Boston and immediately south 



* The suggestions of Professors Woodworth and Jaggar of Harvard and 

 Professor Barrell of Yale University are hereby gratefully acknowledged. 

 Special thanks are due Professor Jeffrey of the Harvard Botanical Labora- 

 tory for identifying the lignites. 



f Final Report on the Geology of Massachusetts, vol. i, pp. xii to 831, 1841. 



% Geology, Chamberlain and Salisbury, vol. iii, p. 260, 1906. 



Am. Jour. Sci. — Fourth Series, Vol. XXII, No. 130. — October, 1906. 



