138 The American Geologist. February, 1894 
tion of the late Tertiary rocks of the Floridian and Gulf region. In 
view of its importance, exact measurements were obtained at the best 
exposures; a triangulation was made for a sketch map, and photographs 
were taken, at Alum Bluff; and tbe western extension of the strata on 
the Chipola river at Bailey's Perry, Abe's Springs, etc., was carefully 
studied. The results show that above the Vicksburg limestone the suc- 
cession of the Miocene rocks is as follows, in ascending order: (1) The 
Chattahoochee limestone; (2) the Chipola marl; (3) the Alum Bluff beds 
(subsequently named Aspalaga clays by Johnson), — in all over 80 feet 
of strata belonging to the older or Chipola (warm water) Miocene; (1) 
the Chesapeake marl; and (5) the aluminous clay, forming the newer or 
Chesapeake (cold water) Miocene, with a thickness of about 80 feet 
more. Above the Miocene strata are about 80 feet of Orange sand, clay, 
and Pleistocene superficial sands. Correlation with this section renders 
it probable that the typical Grand Gulf beds (exclusive of the Pasca- 
goula clays, which seem to be newer Chesapeake) are included in a 
time interval beginning above the lowest Chattahoochee beds and end- 
ing with the epoch of the Alum Bluff sands, thus coming entirely 
within the old Miocene or Chipola epoch. This conclusion agrees in 
the main with the views of. Prof. E. A. Smith as to the probable age of 
the Grand Gulf beds, expressed by him in private letters, as early as 
September, 1892. 
C>. Geological activity of the earth's originally absorbed gases. Alfred 
C. Lane, Houghton, Mich. The argument of this paper is as follows: 
The earth in its early stages absorbed various gases which it is 
now giving off in process of cooling. These gases are an original and 
essential factor in every igneous magma, and their presence is essential 
and characteristic in the crystalline development of plutonic and dike 
rocks, their sudden loss in tbe development of volcanic rocks. When- 
ever cracks extend far enough down into the earth these gases escape 
and carry with them the lava, and so become the moving cause of vol- 
canic eruptions. The earth, below the various surface formations, in- 
creases in basicity and heat toward a core which probably is largely 
metallic iron. Lavas furnished from a crack will be at first a mixture 
of the rock magma at different levels. Their chemical composition will 
vary according to the depth of the crack and other factors, but will be 
of medium basicity as regards the material that can be furnished from 
that crack. Hence any already individualized minerals of pronounced 
acid or basic character, e. a., quartz or olivine, are liable to corrosion. 
Acid lavas might be furnished exclusively by shallow cracks. They 
would have a less high temperature than the basic, and be in a pasty 
condition. The deeper seated basic lavas would have a higher temper- 
ature, hence take a longer time to cool, and so give their vapors more 
time to escape before consolidation. 
The absorbed gases slowly given off from plutonic rocks produce in 
adjacent rocks the characteristic contact zone. In volcanic rocks the 
gases escape from the vent, and hence the contact zone is absent or 
different. These gases are concentrated in the crystallization of plu- 
tonic masses into pegmatitic dikes, so that there is a continuous series 
from pegmatites to segregation veins and true fissure veins filled by 
ascent, allowing the pegmatites to be classed with either veins or igne- 
ous rocks. (The gases are understood, whenever temperature and 
pressure permit, to pass into the state of hot mineralized water.) 
If these gases also percolate with extreme slowness outward every- 
where, we should expect them to tend to produce a regular graduation 
in composition from the center out, causing an exchange of material in 
alternating beds of different composition. The gradual silicification of 
certain older rocks and metamorphism of crystalline schists may in part 
be due to this cause, being like a contact zone for the earth's interior. 
Their action would accentuate the crumpling of the earth's crust by 
