CAPE COD GEOLOGY 



213 



beds on Block Island are greatly contorted little can be said of their strati- 

 graphy or their probable extension from the cliffs into the interior of the island. 

 The beds of clay seen in Clay Head probably extend for some distance back 

 from the cliffs beneath the thick beds of gravel and boulders, but the complex 

 interfolding of the beds of Cretaceous clay with beds of glacial sand and gravel 

 prevents any reliable theoretical projection of the underground structure. 



The higher marine Cretaceous beds that are found on Marthas Vineyard 

 and in New Jersey, as well as the Tertiary beds seen in the cliffs at Gay Head 

 on Marthas Vineyard, are not found on Block Island. This series of beds probably 

 suffered much erosion in this region during pre-glacial time. 



THE LIGMTIC CLAY 



Beds of lignitic clay are exposed, though poorly, beneath a coating of till in 

 the low cliff at Old Harbor. Some years ago, when they were better exposed 

 than they are now, the beds showed anticlinal structure, being much crumpled 

 on their northern limb. The beds cropped out for about 100 feet along the 

 shore. The anticlinal fold contained a layer of friable lignite 6 inches thick. 

 In the northern crumpled part of the section a nearly vertical bed, 3 feet thick, 

 was then seen. Chunks of lignite showing the structure of wood are occasionally 

 found in this cliff. Overlying the bed of dark clay there were beds of sandy 

 clay, which were in places cemented so as to form a reddish, micaceous argilla- 

 ceous sandstone resembling the fragments of drift found in the overlying Pleisto- 

 cene formations. Livermore * states that a substance which appears to have 

 been lignite was found in dredging the harbor many years ago. Beds of lignitic 

 clay and of white kaolinite like that seen in the bluffs at Clay Head probably 

 underlie the island not far below sea-level. 



FOSSIL FLORA 



Hollick 3 has collected from the drifted fragments of Upper Cretaceous beds 

 found in the Pleistocene deposits of the island a dozen species of plants, viz. : 



Gleichenia gracilis Heer. (Plate I, fig. 9.) 



Protophylbcladus subintegrifolius (Lesq.) Berry (Plate V, figs. 1-6). 



Dammara minor n. sp. (Plate II, figs. 35-37.) 



Ficus Krausiana Heer. (Plate X, figs. 1-3.) 



Magnolia woodbridgensis Hollick. (Plate XX, fig. 7.) 



Lauriis plutonia Heer. (Plate XXVIII, figs. 1-2.) 



1 Livermore, op. cit., p. 155, 



2 Hollick, Arthur, The Cretaceous flora of southern New York and New England, U. S. Geol. Survey, 

 Mon. 50, 1906. (See tables on pages 120-128 and the plates and figures indicated in the list.) 



