PHYSICAL GEOLOGY. 177 



follow from this alternations in the direction of concave and convex 

 surfaces. F. D. 



Mallet, R. The Mechanism of Stromboli. Geol. Mag. dec. ii. vol. ii. 

 p. 286. 



Kemarks that what the level of the bottom of the crater may be is 

 immaterial to the validity of his theory (see Judd, p. 174). 



Mohr, Prof. — . Ueber die Ursache der Erdwarme. N. Jahrb. 

 pp. 371-377. 



Discusses the observations of underground temperature made in a 

 bore-hole at Spereraberg, 5^ miles S. of Berlin, carried to a depth of 

 4042 feet. The rate at which the temperature increases lessens with 

 the depth, the increase of temperature for any 200 feet being 0°-05 R. 

 less than for the 200 feet immediately above. If this law held good 

 for all depths, the temperature would cease to increase beyond a depth 

 of 5170 feet. Argues from these facts that the heat of the crust 

 cannot come from the interior, but must be generated in the superficial 

 portion by chemical action and similar causes. A. H. G. 



Neumayr, Dr. M. Die Aralo-Kaspi-Niederung. [The Aralo-Caspian 

 Depression.] Verh. h.-k. geol. Reichs. Bd. xxv. pp. 31—33. 



Controverts Prof. Schmick's views as to oscillation of sea-level and 

 recurring periods of warmth as applied to this locality. 



Noak, F. W. Ueber die Bildung der Continente. [Formation of 

 Continents.] N. Jahrb. Heft ix. pp. 897-925 ; 2 woodcuts. 



In seeking to explain the present distribution of land and sea, goes 

 back to the period of igneous fluidity, and discusses-the effects of strains 

 upon the solidifying crust. The pressures were due partly to contrac- 

 tion on cooling, partly to a tidal wave in the interior. A narrow- 

 meshed network of cracks first formed; then fissures filled with ejected 

 matter, which re-cemented the fractures ; a new system of cracks would 

 afterwards be formed, but as the crust became stronger the fissures 

 were fewer and further apart, till at length a colossal line of fracture 

 would encircle the earth. Illustrates his theory by seeking to explain, 

 by means of diagrams, the formation of the American continent. 

 Before dry land appeared in the American area, a great meridional 

 cleft was formed ; the tidal wave in the interior passing from E. to W. 

 forced molten matter into this crack, which closed and re-opened, 

 and trachytic ejecta formed the nucleus of the Andes and Rocky 

 Mountains. By the action of the wave from E. to W., a large tract of 

 country was ultimately raised above water E. of the back-bone of the 

 continent, but none on the W., as pressure was relieved by eruptions. 

 Three principal lines of volcanic activity are traced : — 1, Old World ; 

 2, America ; 3, Pacific system. The author supports his theory by 

 reference to ancient myths. F. W. 11. 



Parton, T. Disturbing forces underground. S. Staff. Sf E. Worcester. 

 Inst. Min. Eng. 



Pfaflf, — . [Expansion of Rocks by Heat.] Zeitsch. deutsch. geol. Oes, 

 t. xxxiv. p. 401. 



1875. N 



