272 
IOWA ACADEMY OF SCIENCE 
CONTRAPOSED SHORE LINES ON STRAITS OF 
JUAN DU FUCA. 
CHARLES KEYES. 
{Abstract.) 
Among the many novel geologic phenomena to which was 
directed the attention of those who took part in the trans-con- 
tinental excursions of the Twelfth International Geological Con- 
gress, convened in Canada a year ago, were some remarkable 
examples of the exhuming of old and buried shores of the Pa- 
cific ocean in the vicinity of Puget Sound. 
In late geological times there has been more or less constant 
rising and sinking of the coast. In a previous geographic cycle 
a very resistant igneous rock had been cut into by the waves 
so as to form a low sea-cliff. By subsequent slight sinking this 
cliff and shore were carried below tide-level, and covered by 
sands and gravels. Today, with marked coastal uprising, a 
new shore line is being developed, the old shore line being un- 
covered at the same time. 
As a special term to express the idea of the development of 
this type of shore line, which is in every way analogous to the 
formation of the superposed river valley Clapp has proposed 
the title ‘‘Contraposed Shore-lines”. On the borders of the 
straits of Juan du Fuca, which separate the island of Vancouver 
from the state of Washington the phenomenon is so clearly dis- 
played that photographs show every characteristic. 
