56 



CAPE COD GEOLOGY 



and probably higher beds of the Manhasset formation, such as beds of outwash 

 glacial sand, were removed. 



VINEYARD INTERGLACIAL STAGE 



The Vineyard interglacial stage probably covers the time of the following 

 events in the Mississippi Valley, in chronologic order: Sangamon interglacial 

 stage of Leverett, Iowan stage of glaciation of Iowa geologists, and Peorian inter- 

 glacial stage of Leverett. 



The Wisconsin drift lies unconformably upon all the Pleistocene and older 

 formations already described. Shaler appears to have recognized an eroded old 

 land surface of pre- Wisconsin date in his report on the geology of Marthas Vine- 

 yard, when he still regarded the pre-Wisconsin drift and the older formations of 

 the island as Tertiary. He writes : 1 



The form of the surface of the Tertiary [sic] beds compels me to believe that they retain 

 in good part the shape which they had before the beginning of the last glacial period. If we 

 could remove all the glacial waste from this surface we should find that it had a contour closely 

 resembling that of the chalk downs in southern England. We should see broad, rolling hills 

 sloping gently down to infrequent valleys, a topography characteristic of a land surface where 

 rain, frost, and stream had long and steadily acted upon beds of the uniform nature which 

 characterizes the Vineyard series. 



In 1897 Shaler again described this erosion surface, giving additional in- 

 formation gained from a resurvey of the island. Its date was fixed as later than 

 that of the deposits here described as the Manhasset formation and earlier than 

 the Wisconsin stage. He assigned not only the erosion of the valleys in the up- 

 lands of Marthas Vineyard to pluvial action at this stage but also the excavation 

 of the neighboring sound; and he estimated that the time indicated by this 

 erosion was twenty times as long as the interval between the present day and the 

 disappearance from the island of the last ice sheet. 2 



In 1897 I presented further evidence relating to the epoch of interglacial 

 erosion that preceded the Wisconsin moraine, showing the beheadal and capture 

 of streams and the partial adjustment of streams to the folding of the older beds 

 on Marthas Vineyard, and I proposed the name Vineyard interval for this epoch. 3 



In the same paper traces of the Vineyard stage of erosion by running water 

 were reported to be recognizable beneath the drift and traces of the action of 

 Wisconsin ice on Block Island. Still later, in 1901, the same erosion surface was 



1 Shaler, N. S., Report on the geology of Marthas Vineyard, Seventh Ann. Rept. U. S. Geol. Survey, 

 p. 328, 1888. 



2 Shaler, N. S., Tertiary and Cretaceous deposits of eastern Massachusetts, Bull. Geol. Soc. America, 

 1, p. 448, 1890. 



3 Woodworth, J. B., Unconformities of Marthas Vineyard and of Block Island, Bull. Geol. Soc. 

 America, 8, pp. 208-209, 211-212. 



