The American Geologist. August, 
graphical distribution of the rock and also the divergent 
views concerning the genesis of the discrete pillow-structure.* 
A-s a supplement to his summary, the following table lias been 
prepared, showing the already determined main facts and con- 
clusions regarding the origin, geological age, associated sedi- 
ments, and variolitism of the principal occurrences. 
The later writers have taken contrasting views of origin, 
which, however, have this point in common, that the pillow- 
structure is to be connected with the presence of abundant 
moisture at the surfaces over which the flows occurred. Teall, 
Ceikie and Platania credit the phenomenon to submarine erup- 
tion whereby the lava has flowed either directly into water or 
has been intruded into the water-soaked oozy silt of the sea- 
bottom. Ransome has stated his belief that the structure is not 
confined to surface-flows but may be found in dike-like masses 
intruded near the surface of a rock-series now represented by 
radiolarian cherts and by sandstones. Clements, on the other 
hand, compares the Michigan ellipsoidal basalt to the aa lava of 
Hawaii and Santorin and rejects Teall's hypothesis of a sub- 
marine origin. The following- quotation is taken from the 
Crystal Falls monograph. "Roth Ransome and Teall compare 
the ellipsoidal basalts with pahoehqe lava. The latter also 
suggests a submarine origin for the basalts studied by him. 
It should be noted that pahoehoe lava in its typical occurrence 
in Hawaii is found only in dry places, whereas the aa is 
confined to those parts of the lava stream — which in other parts 
of its course is perhaps developed as pahoehoe — where it cros- 
ses moist valleys or other depressions presumed to have con- 
tained a considerable amount of moisture. 
"In the case of some of the block lava of Santorin described 
by Fouque. with which this may be compared, the conditions 
were such that the lava practically welled up through the 
water. 
"From Dana's description it appears that lava in the pa- 
hoehoe form can not exist in the presence of moisture, being 
changed to the aa form. R would thus seem that Teall's state- 
ment of a submarine origin for the pahoehoe lava is untenable.""!' 
The grounds for Clements' rejection of the submarine hy- 
pothesis do not seem satisfactory to the present writer. The 
* Monograph xzzW, U. S. Geol. Surr., 1899, p. 118. 
f Clk.mknts. Op. cit., p. 123. 
