THE 
AMERICAN GJiOLOGIST. 
Vol. XXVII. JANUARY, 1901. No. 
BREVITY OF TUFF-CONE ERUPTIONS 
By S. E. Bishop, Honolulu. 
PLATE I. 
Tuff-cones, of which a number have been formed on the 
eastern coasts of the island of Oahu, are produced by the class 
of eruptions distinguished as " explosive." The semi-liquid 
tuff has been projected in a jet or fountain to a considerable 
distance and having been driven laterally by the expansion of 
the steam and other gases contained, has fallen at some dis- 
tance from the vent, building up a cone with a more or les;. 
regular rim enclosing a concave bowl. All the explosive 
eruptions actually observed seem to have occupied a very 
brief time. The greatest one, that of Krakatoa, was probably 
less than one hour in actual emission, although the fall of its 
lighter ejecta continued for several hours. 
It therefore seems remarkable that an opposite opinion 
should have been expressed respecting the eruption which 
produced Diamond Head. This typical tuff-cone, lying in 
the suburbs of Honolulu, bounds our ocean view to the east- 
ward. It was recently examined by Doctor W. H. Dall of the 
Smithsonian Institution with especial regard to the age of 
the fossil shells found in its debris. In the "Bulletin of the 
Geological Society of America," Volume 11, pp. 57-60, Dr. 
Dall expressed conclusions respecting the age of the crater, 
which I feel obliged to controvert. He says : 
"The conclusion to which I came was that the whole mass 
of Diamond Head had been slowly deposited in comparative- 
ly shallow water and gradually elevated without being sub- 
jected to notable flexure The ejection of material at first 
