230 DYNAMICAL GEOLOGY. 



even in the Florida Straits. Over a portion of the *•' Blake plateau," a region 

 southeast of Georgia, between the lines of 100 and 600 fathoms, the bottom 

 is " clean of mud and ooze, and almost so of living species " ; and A. Agassiz 

 has hence suggested that abrasion by current action may be going on over 

 it. It is a question for investigation. 



The bottom of the Atlantic Ocean, south of Newfoundland and thence 

 southwestward, has received droppings of stones, gravel, and earth from ice- 

 bergs, and the deposits of the Glacial period extend some distance south of 

 the latitude of Cape Hatteras. They consist of sand, stones, and some large 

 bowlders of granite and other rocks. The " Challenger " expedition dredged 

 up a 500-pound bowlder of syenyte in this region near latitude 41° 14' W., from 

 a depth of 1340 fathoms (Murray, 1885). The "Albatross," of the United 

 States Fish Commission, obtained granite bowlders of 50 pounds near 71°- 

 72° W. and 37° 40' N. (Verrill, 1884). In the Glacial period, even New York 

 Bay, and perhaps Delaware Bay, discharged icebergs for transport by the 

 Labrador current to a melting region on the borders of the Gulf Stream. 

 On the east margin of the Gulf Stream, in 2000 fathoms, the dredge has 

 found, as Verrill states, only the usual Globigerina ooze, and farther south 

 toward the West Indies, the bottom is no less free from continental debris. 

 But the modern era has its new element, which has made exceptions pos- 

 sible over all the ocean. 



Owing to the presence of Man in the world, whose life is on the waters 

 as well as the land, the bottom deposits have been found in one case to afford 

 a dredge-load of red bricks. It was brought up from a depth of 1537 fathoms 

 (nearly 10,000 feet) in the Atlantic in latitude 39° 3' and longitude 70° 51' ; 

 and Professor Verrill, the reporter (1884), remarks that the bricks were 

 probably from the used-up furnace of a returning whaler, and Avere thrown 

 overboard when nearing home after a whaling voyage. 



We are led by the facts to the belief that in the cold, dark, still, abyssal 

 depths, through which transportation is reduced to descent by gravity, ooze, 

 sprinkled with volcanic ashes for concretion-making, is the substitute for 

 sand, gravel, and mud ; and where the means of biological progress are 

 simply strife for food and mate and physiological response to living work, 

 there is excessively slow and feeble geological change. 



III. FREEZING AND FROZEN WATER: GLACIERS, ICEBERGS. 



Water performs part of its geological work in the act of freezing, and 

 another part when frozen, in the condition of snow and ice. 



Water Freezing. 



1. Displacement and fracturing. — Since water on becoming ice, at 32° F., 

 increases in volume about y^j-, or lineally about Jg-, and diminishes in density 

 to 0-92, whenever freezing takes place in crevices, it opens and deepens them, 



