CAPE COD GEOLOGY 



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any great distance horizontally. The gravel and sand are typical waterlaid 

 glacial deposits derived from granitic rocks. The material in the gravel consists 

 of quartz, fairly fresh feldspar, and other minerals. In addition to these finer 

 constituents there are small pebbles, chiefly of igneous and metamorphic rock, 

 and a small percentage of pebbles of sedimentary rock. Some of the pebbles 

 were obviously derived from the earlier Pleistocene deposits and show consid- 

 erable weathering, but the greater part of them are fresh and are typically 

 waterworn. The sand in the Herod gravel consists largely of grains of quartz 

 but includes small amounts of other minerals. Where the Herod gravel overlies 

 a depression in the surface of the Jacob sand or the Gardiners clay it has been 

 strongly stained, because the relative imperviousness of the underlying beds 

 has allowed the water that seeped down through the overlying beds to collect 

 and remain long enough to deposit some of the material that it contained in 

 solution. Much of the material carried in solution by this water was probably 

 derived from the Montauk till, some of whose constituents are very finely ground 

 and evidently somewhat soluble. Even at present the water in wells in the region 

 where the Montauk is found contains oxides of iron. The staining material is 

 usually brown or red, but at some places, as at Norton Point, its color may be 

 a bright orange-yellow, or it may be nearly black. 



Thickness. — The thickness of the Herod gravel differs greatly from place 

 to place according to the extent of its erosion by the ice, as well as according to 

 the probable original differences in it at the time of its deposition. Where no 

 Montauk till overlies the Herod gravel it grades imperceptibly into the Hemp- 

 stead gravel, which at such places cannot be distinguished from the Herod. 

 The combined thickness of the two beds may therefore be mistaken for the 

 thickness of the Herod alone. The maximum thickness of the Herod gravel, 

 seen in Nashaquitsa cliffs, is about 100 feet. Elsewhere its thickness is much 

 less. 



Structure. — The Herod gravel is usually bedded, the beds consisting of layers 

 of coarser and finer material. Many of the beds are horizontal, but where the 

 whole member has been disturbed the beds conform to the distortion of the 

 formation as a whole. The Herod gravel is probably made up of lenses of gravel 

 and sand. The sand is in places 20 feet thick and contains no layer of gravel. 



The Herod gravel as a whole, especially on the Vineyard Sound side of the 

 western area, has been deformed by the Montauk ice, the deformation consisting 

 largely of gentle folding and warping. The beds do not show the well-defined 

 small foldings shown by beds of clay, their tendency under pressure being to 



