466 
Van Hise—Earth Movements. 
in volcanic phenomena. It has been supposed by Russell 1 that 
some of the great mountain uplifts of the United States are due 
to the interior transfer of molten material. If this be so, the 
question remains as to the cause of the transfer. For such 
transfer reasons are later assigned. Some of the intruded igne¬ 
ous material, long after solidification, has reached the surface 
by the removal of the covering rock through epigene agencies. 
Probably a much greater part still remains below the surface. 
That the lithosphere locally has movements which we call 
earthquakes is well known. It is not so well known that minor 
tremors continuously affect much or all of the surface of the 
earth, 2 but the majority of these tremors are so feeble as not to 
be called earthquakes, even by scientists who classify as earth¬ 
quakes many very slight shocks which the senses do not detect. 
But even the most violent earthquakes are very insignificant 
rock waves, being only a few centimeters in amplitude, and the 
permanent effects of earthquakes upon the earth are compara¬ 
tively slight. It is of course well known that in some cases 
volcanoes and earthquakes are most disastrous to the living 
things which chance to occupy the disturbed tracts. 
With the exception of earthquakes and active volcanoes, we 
are accustomed to think of the lithosphere as motionless. Yet 
these phenomena are far less important than other existing earth 
movements. As in so many cases, the exceptional has attracted 
the greater share of attention, while the slow, general move¬ 
ments have escaped notice. 
The latter earth movements may be classified into mass move¬ 
ments and molecular movements. The mass movements are ver¬ 
tical and horizontal. As a result of the vertical mass move¬ 
ments the continents are now above and now below the waters 
of the ocean. Such movements were named by Gilbert epioro- 
genic. As a result of the vertical and horizontal mass 
movements combined, mountain ranges here and there on the 
1 Igneous intrusions in the neighborhood of the Black Hills of Dakota, 
by I. C. Russell: Journ. of Geol., Vol. IV, 1896, pp. 23-43; On the nature 
of igneous intrusions, Ibid., pp. 177-194. 
v 2 Popular lectures and addresses, by Lord Kelvin: Vol. Ill, 1891, 
pp. 158-9. 
