94 SURFACE GEOLOGY. 



The description of the ordinary aUuvial terraces and plains of the Mer- 

 rimack was interrupted at the mouth of Soucook river. Thence nearly to 

 Manchester the average width of the alluvial area is about one mile. Its 

 narrowest place is at Hooksett, where ledgy hills rise close to the river 

 on both sides. The Pinnacle, a sharp peak of white quartz on the west, 

 350 feet above the river, affords a very beautiful view of the valley north 

 and south, including several villages. The most interesting portion of the 

 alluvium is its highest terraces. These are from 100 to 125 feet above 

 the river, and are usually well shown upon both sides. Their similarity 

 in height on opposite sides and their very steep escarpments facing each 

 other, as already frequently pointed out, indicate their formerly continuous 

 extent. These upper terraces form wide plains in Bow, which have been 

 partly eroded by Moore's brook, and in Hooksett, south of the Pinnacle 

 and north from Martin's ferry. The last of these areas extends back at 

 the north one mile from the river. The greater part of its material is 

 coarse gravel, and its origin seems to have been from the north-east at 

 the time of the departure of the ice, differing from the ordinary fine allu- 

 vium, which was slowly deposited from the floods of the main valley. 



Valuable beds of clay, extensively used for brick-making, occur in the 

 highest terrace for four miles north from Hooksett, upon the east side. 

 This clay appears to form a nearly continuous stratum, which has a thick- 

 ness of from 20 to 30 feet, with its top about 100 feet above the river. 

 It is overlaid by a few feet of sand. The upper part of this stratum con- 

 sists of a hard and compact ^wj/ clay. At a depth of 10 to 15 feet this 

 is usually separated, by a thin layer of sand one fourth of an inch to three 

 inches thick, from the underlying bhie ^/^rj/, which is soft and plastic when 

 dug from the bank. A gradual transition from the gray to the blue clay 

 is rarely seen. These divisions are nearly equal in amount, but in some 

 of the brick-yards only the upper gray clay is exposed. Except the lower 

 part of the blue clay, which is of inferior quality, both layers are well 

 adapted for brick-making. 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 the Hudson river and Lake 

 Champlain.* Two miles above the most northerly of these brick-yards, a 



* Natural History of New York, Mather's Geology of the First District, \>. 128, etc., and Hitchcock's Geology 

 nf Vermont, pp. 157, 160, etc. 



