336 THE CANADIAN NATURALIST. [Vol. viiL 



of the upper terrace, or of still higher tributary deltas. These 

 areas are generally of a clayey, moist, productive soil, quite iu 

 contrast with the dry and sandy " pine-plains" of Merrimack 

 river, Ossipee lake, and other parts of the State. The modified 

 drift of the Merrimack is usually one to two miles wide ; its 

 greatest development is in Concord, and in Litchfield and Merri- 

 mack, where it has a width of nearly four miles. 



Valuable beds of clay, extensively used for brick-making, 

 occur in the highest terrace on the east side of Merrimack 

 river for four miles north from Hooksett. This clay appears to 

 form a nearly continuous stratum, which has a thickness of from 

 20 to 30 feet, with its top about 100 feet above the river, or 

 300 feet above the sea. It is overlain by a few feet of sand. 

 The upper part of this stratnm consists of a hard and compact 

 gray clay. At a depth of 12 to 15 feet, this is usually separated 

 at a definite line from the underlying Hue clay, which is soft and 

 plastic when dug from the bank. Deposits of the same gray 

 and blue clay, the latter always below the former, are frequently 

 found in the south-east part of the State, near the coast, and 

 along Hudson river and Lake Champlain. These clays and the 

 overlying sand are probably equivalent to the Leda clay and 

 the Saxicava sand, distinguished by Principal Dawson in the 

 St. Lawrence valley. 



The only marine shells that have been found in New Hamp- 

 shire, occur in these beds near the coast, and show that the sea 

 stood at least 150 feet higher than now during the deposition of 

 the modified drift. Bones of a seal and shells of Leda truncata 

 are found at South Berwick, Maine, 30 feet below the surface, 

 and nearly 1 00 feet above the sea. The surface here is a few 

 feet of sand, the whole depth below which is clay, the upper 

 portion gray, and the lower blue. Saxicava rvgosa, Mytilus 

 edulis, and Astarte castanea occur atseveral places in Kittery, 

 Maine, within 30 feet above the sea. These towns border New 

 Hampshire. The most southern locality at which Leda truncata 

 has been found is Portsmouth, New Hampshire, where it ocenrs 

 15 feet below the surface, and 30 feet above high tide, in blue 

 plastic clay- This species is now restricted to arctic seas, and 

 its occurrence in Portsmouth and South Berwick shows that an 

 arctic climate prevailed during the deposition of the beds in 

 which it is found ; but the presence of Astarte castanea at Kit- 

 tery is proof that the ocean became nearly as warm as now before 

 it s ank to its present level. 



