656 DYNAMICAL GEOLOGY. 



are only slightly compacted, or are unaltered. Fig. 1095 is a reduced 

 view of a layer thus plicated, from the Post-tertiary of Booneville, 

 N. Y. Vanuxem illustrates the facts there observed by him, with 

 this and other figures (N. Y. Geological Report), and attributes the 

 plications to lateral pressure, while the layer was in a softer state 

 than those contiguous. 



2. Mud-lumps, Mud-volcanoes. — The shallow waters within one to 

 three miles of the main channel or mouth of the Mississippi River 

 (see map, p. 652) are dotted with what 'are called mud lumps, — con- 

 vex or low-conical elevations, sometimes 100 feet or more in diameter, 

 — showing their tops at the surface. They originate in upheavals 

 of the soft bottom. Once formed, they discharge mud from the top, 

 which gives to the material of the low cone the structure of a volcanic 

 cone, the successive layers being, however, of mud, and but a fraction 

 of an inch thick. They finally collapse ; and then the cavity of the 

 cone sometimes becomes the site of a pool of salt-water, like the lake 

 in an extinct volcano. They are formed, according to Prof. E. W. Hil- 

 gard (from whose description in the " American Journal of Science," 

 III. i., the facts here given are cited, and who adopts, in the main point, 

 the view of Lyell), through the pressure of the surface deposits on a 

 layer of mud which overlies the Port Hudson clay, or Champlain al- 

 luvium (p. 547). Some carbo-hydrogen gas is given out, arising from 

 the decomposition of animal or vegetable matters in the mud. 



3. Moisture confined in Rocks. 



The amount of moisture in different rocks varies with their kinds 

 and compactness of texture. 



In 1853, Durocher published some results of experiments with regard to the amount 

 of water contained in different crystallized minerals, giving, among them, "0028 to 

 •0269 per cent, for orthoclase, or common feldspar; -0127 for porphyry; "0203 for 

 euryte, a feldspathic granyte, etc. Delesse made further examinations of rocks, in 

 1861, and found the amount of moisture in coarse granyte 0-37 per cent ; in euryte, 

 O07; in milky quartz, from a veiu, 0-08; in flint, from the chalk at Meudon, - 12; in 

 a compact Tertiary limestone (Calcaire grossiere), 3-11; in chalk, from Meudon, nearly 

 20 per cent. ; in a quartzose sandstone (gres de Fontalnebleau, near Meudon), 2*73. 

 Hunt, in some experiments, the results of which were published in 1865, obtained 

 for the amount of moisture absorbed, after drying at a temperature between 150° and 

 200 3 F. : for Potsdam sandstone, three specimens, 2-26 to 2-71 per cent.; other three, 

 6'94-9 - 35; for Trenton limestone, 032 to 1*70, the former for a black variety; for the 

 Chazy rock, an argillaceous limestone, 6 '45 to 13 - 55; a ciystallized dolomite, of the 

 Calciferous formation, four specimens, 1-89 to 2-53; two other specimens, 5 - 90 to 7 "22; 

 for the Medina argillaceous sandstone, two specimens, 8-37 to 10-06. l 



The facts, as first suggested by Saemann, early in 1861, and after- 

 ward at more length by Delesse, show that the thickening of the 



1 Durocher, Bull. Soc. Geol, x. 431, 1853; Delesse, ibid., xviii., 64, 1881; Hunt, 

 Amer. Jour. Sci., II. xxxix. 193. 



