324 The American Geologist. ^^J'- 1904. 
there are not indications in the conditions surrounding these 
volcanic necks that allow or require that such necks were also 
thrust upward in a solid, or at least semi-plastic, condition 
from some depth below. Does not the vertically columnar 
structure exclude the idea of cooling from the sides of a fissure 
or pipe ? May not such vertically columnar necks be the deeper 
portions of non-columnar original peleliths which moved up- 
ward originally in the same manner as the peak at Mont Pele. 
It is apparent that the pelelith must graduate downward into 
less and less solid igneous rock and that such rock in slowly 
cooling would not only not be holocrystalHne, but would be- 
come structurally basaltic in a direction parallel to that in 
which its heat departed, i.e., toward the mouth of the crater. 
If the slow extrusion continued such columnar rock would 
finally appear above the crater and might be thrust upward to 
a considerable hight, and might stand long after the upper 
non-columnar, or less columnar, summit had decayed and dis- 
appeared. The surroundings and structure of the peak of Mt. 
Taylor, in New Mexico, seem to allow of such explanation,* 
although the subordinate peaks, at a much lower level, have 
doubtless been uncovered as explained by captain C. E. Button. 
Another beautifully columnar volcanic neck is that of Mato 
Teepee in South Dakota. It stands in the valley of the Belle 
Fourche, about 55 miles in an air line northwest of Deadwood. 
It rises 1126 feet above the river.f It is a great rectangular 
obelisk of trachyte with a columnar structure, giving it a ver- 
ticallv striated appearance, as shown by plate xxii. It rises 
625 feet about perpendicular from its base. It has been de- 
scribed by professor I. C. Russell in the Journal of Geology, 
vol. 4, p. 31, who gives abundant evidence that as it appears at 
the present time it has been brought to light by the removal of 
sedimentary strata in the midst of which it rises, 1500 feet of 
which have been eroded. He gives, however, no sufficient evi- 
dence that this "plutonic plug" did not terminate in an active 
volcano. Its date was perhaps mid-Cretaceous, but even if 
it were mid-Tertiary, the surface products of such a volcano 
would long since have disappeared under the vicissitudes of 
such vast erosion as he shows has taken place in the valley of 
* Mt. Taylor and the Zuni plateau. C. E. Dutton. Sixth Annual Report 
of the United Geological Survey. 
t Geology of the Black Hills. Hhnry Newton. 
