MARINE! WATERS 159 



The supposed absence of marine fossils in the Hudson Valley is doubt- 

 less due to the freshening of the waters by the copious glacial and land 

 drainage. Until the episode of the Second Iroquois the flood of glacial 

 waters of the St. Lawrence Basin was poured into the Hudson Inlet at 

 Schenectady. During the Second Iroquois the glacial flood was merely 

 shifted to the north, and during all the long life of the Hudson-Cham- 

 plain Inlet all the fresh waters were forced south. However, marine 

 fossils are abundant in the Champlain Valley and are found at altitudes 

 the planes of which carry over the Fort Edward Divide into the Hudson 

 portion of the great valley. 



The detrital deposits formed in the marine waters are large in volume 

 and area. Up the Hudson as far as Catskill the terraces of clay and sand 

 are very conspicuous and afford the materials for brick manufacture on 

 an immense scale. North of Catskill, in the widening valley, the summit 

 sand plains lie back from the river, though lower terraces may yet be 

 seen. While much of the deeper deposits and those in the middle of the 

 valley or beneath the present waters are of glacial origin, the heavy visible 

 deposits are chiefly the deltas of tributary land streams, the greatest 

 being that of the Iromohawk at Schenectady- Albany. 



From Troy to Glens Falls the borders of the lower valley are buried in 

 a deluge of sand, sloping down in terraces toward the axis of the valley. 

 Saratoga lies in the midst of a vast area of detrital marine accumulations. 

 The slow lifting of the valley out of the waters gave the latter an excel- 

 lent chance to produce level stretches and conspicuous terraces, the latter 

 being more prominent as the steeper slopes approach the middle of the 

 valley. The Champlain portion of the great valley also holds vast sand 

 plains, especially on the larger rivers, as the Ausable, Saranac, and Big 

 Chazy. 



Epeirogenic Movement: Diastrophism 



The great changes in altitude of the surface of the State, both before 

 and since the glacial occupation, has already been noted. The relation 

 of the land movement to the burden of the ice-cap should be briefly dis- 

 cussed. If the earth's crust is sensitive to long-continued pressures, then 

 the thickness and weight of the ice-body become an important matter. 



Again, our lack of knowledge of the duration and diastrophic effects 

 of the pre-Wisconsin ice-caps limits our discussion to the effects of the 

 Laurentian ice-body. 



At its maximum the thickness of the ice-cap over the Adirondacks and 

 the Champlain Valley was probably not less than 10,000 feet. This is 

 equal in weight to over 3,000 feet of rock. Southward the ice decreased 



