84 
DYNAMICAL GEOLOGY 
of the earth’s crust in the latitude of Denmark in the same period, 
having the secular retardation of the earth’s rotation as a con¬ 
trolling factor. Rough guessing seems to indicate close agreement. 
The amount of stretching now appears mainly ascribable to sec¬ 
ular polar bulging. 
Before implicit acceptance at its face value of stretching of the 
Copenhagen base line as evidence of polar expansion effects the 
phenomenon will have to be geologically analyzed with special 
reference to the possibility of telluric stress release along cir¬ 
cumscribed belts or along fault lines. We gather something of 
the modus operandi from consideration of the rifting which pro¬ 
duced the San Francisco earthquake of 1906. Below Point Reyes 
where the movement was greatest and amounted to ten or twelve 
feet, the horizontal component is indicated by the off-setting ef¬ 
fects of fences, roads, and even buildings. In order to determine 
possible future movements however slight, the University engin¬ 
eering corps planted stone monuments at certain points on either 
side of the rift. 
The San Francisco movement is in mountainous country; and 
all lines in mountainous tracts obviously have to be excluded from 
polar bulging calculations. Only great plains situations are enter¬ 
taining. In the case of the Copenhagen base-line possibility of 
its crossing not an actual rupture but a line of crustal strain has 
yet to be excluded. 
The stretching of the Danish base-line is worthy of most careful 
inspection with regard to its telluric affinities. 
Kkyes. 
Composite Nature of Rock Mass-movement. Under its environ¬ 
mental forces the solid earth, the popular symbol of strength and 
permanency, proves weak and incompetent. The crust bends, 
crumples, breaks, and mashes. In an engineering sense the lithos¬ 
phere fails; in considerable part it now consists of structural 
ruins. 
Movements of rock-masses within the zone accessible to obser¬ 
vation are accomplished by fracture and flowage. These processes 
may be distinct and separate, or so inter-related as to make defi¬ 
nition difficult. The zones of movement are many; their positions 
and attitudes diverse. In general, they indicate shearing or grind- 
