GEOLOGY. 291 



stone, the material of \vhich the Smithsonian Institution is construct- 

 ed, 2,691 ; alum limestone, 2,334 ; Stockbridge marble, 2,251 ; Aquia 

 Creek sandstone, the worthless material of which the Patent-Office is 

 constructed, 1,660; common brick, 1,000. In three trials of the alum 

 limestone made by Dr. Page, an average strength of only 1,521 pounds 

 was obtained, while the mean of four trials of Aquia Creek sandstone 

 gave an average strength of 1,000 pounds, thus showing the inferior- 

 ity of at least some portions of the material used in the Washington 

 Monument to the Aquia Creek sandstone, which is acknowledged to 

 h-3 among the worst building materials to be found in the country. 

 Prof. Johnson also gives a large number of tables showing the com- 

 parative strength of many of the ordinary building materials in this 

 country and Europe, in comparison with all of which the alum lime 

 stone is greatly inferior. A 1.5 inch cube of Quincy sienite, the 

 stone of which Bunker Hill Monument is built, sustained a crushing 

 force of 15,929 Ibs. per square inch ; the average of two trials by Dr. 

 Page on 2-inch cubes of alum limestone, gave a resisting force per 

 square inch of only 2,334 Ibs. The following table shows the relative 

 value of several kinds of stone, as determined by their power to resist 

 crushing, the value of the alum limestone being assumed as 100. 



Porphyry, . . . 1, 266 1 Chester (N. Y.) marble, . 171 

 Swedish basalt, . . 1,165 Bagneaux stone (Pantheon, 



Auvergne basalt, . . 703 



Quincy sienite, . . . 682 



Oriental rose granite, . 536 

 Blue granite of Aberdeen, 



Scotland, . . . 468 



White-veined Italian marble, 414 



Purbeck stone, England, . 392 



Baltimore granite, . . 267 



Travertine of Ancient Rome, 183 



Paris) , . 



Temple of Psestum stone, . 130 

 Patapsco granite, . . 118 

 Seneca sandstone (Smithso- 

 nian Institute), . . 115 

 Alum limestone, . . .100 

 Stockbridge marble, . . 96 

 Aquia Creek (Patent-Office) 

 sandstone, . . .71 



It is but fair to state, that the alum limestone is used as the external 

 casing only of the Washington Monument, a more durable stone hav- 

 ing been chosen for the interior. 



ANCHOR-ICE. 



WATER sometimes freezes upon stones below the unfrozen surface 

 of the water ; fastened in this way, it passes under the common name 

 ef anchor-ice. As soon as the ice is detached , it rises to the surface 

 and floats upon it. In explaining this phenomenon, it has been said, 

 that, in thus freezing, the water parts with its latent caloric to the 

 stone and crystallizes upon it, and that its crystals are then heavier 

 than water. The first part of this solution is only a statement of the 

 fact in chemical language, and the last part is opposed by the fact that 

 the detached ice uniformly and directly rises to the surface. The ob- 

 served facts are the following. Anchor-ice forms in still or running 

 water, and often where the current is rapid, on stones, and on wood, 

 fresh or old, under water, in masses from less than an inch to two or 



