191 1.] REID— ISOSTASY AND MOUNTAIN RANGES. 447 



servations made across the United States, which led them to the 

 conclusion that isostasy was true only in so far as the very largest 

 features of the earth's crust, such as the continents and ocean basins, 

 were concerned, but that mountain ranges were at least in part sup- 

 ported by the rigidity of the crust. 



When Dr. Nanscn drifted across the North Polar basin in the 

 Fraiii he provided pendulums to determine the force of gravity 

 when the ship was frozen in ice ; and the discussion of his observa- 

 tions showed that gravity was normal over that basin, or, at least, 

 where his observations were made.* 



Professor Helmert,^ in Germany, has done much in the discus- 

 sion of gravity measures and Dr. Plecker has made some notable 

 voyages and has determined the forces of gravity at sea, over the 

 Atlantic, Indian and Pacific oceans, and over the Black Sea, the 

 results showing that on the whole the force of gravity is normal 

 over these bodies ; only in special and limited areas, in the neighbor- 

 hood of very steep slopes, was any marked anomaly found." 



But the most important work which has been done along this 

 line is the work of Dr. John F. Hayford,' who, while connected with 

 the United States Coast and Geodetic Survey, discussed in a thor- 

 ough and able manner the deflections of the vertical at a large num- 

 ber of stations in diiTerent parts of the United States, and his results 

 show definitely that over this region isostatic eciuilibrium actually 

 exists. He has concluded that this is true even for areas as small 

 as a square degree, that is, seventy miles on the side. He believed 



* " The Norwegian North Polar Expedition of 1893-96," Volume II., 

 Part VIII., Results of the PenduUun Observations, bj^ E. O. Schiotz. 



° " Hohere Geodesie," Leipzig, i&So. 



'" Bestimmung der Schwerkraft auf dem Atlantischen Ozean," I'croff. 

 des Konig. Preuss. Geodet. Instit., Neue Folge, No. 11. "Bestimmung der 

 Schwerkraft auf dem Indischen und Groszen Ozean," Veroff. des Zentral 

 Bureaus der Interuat. Erdmessiing, Neue Folge, No. 18. " Bestimmung der 

 Schwerkraft auf dem Schwarzen Meere," same. No. 20. 



'"The Geodetic Evidence of Isostasy, etc.," Proc. JVashingtoii Acad 

 Sci, 1906, Vol. VIIL, pp. 25-40. "The Earth a Failing Structure," Bull. 

 Philos. Soc., Washington, 1907, Vol. XV., pp. 57-74. " The Figure of the 

 Earth and Isostasy," United States Coast and Geodetic Survey, 1909. " Sup- 

 plementary Investigation in 1909 on the Figure of the Earth and Isostasy," 

 same, 1910. " The Relation of Lsostasy to Geodesy, Geophysics and Geology," 

 Science, February 10, 191 1, 



