702 
mass of heated ground here is about 500 feet 
long by 20 feet wide, and the action reaches 
a depth of perhaps 15 or 20 feet. Blue smoke, 
which contains a high percentage of sulphur- 
dioxide, issues from vents in the mass, and 
fragments of wood inserted in these are read- 
ily charred and consumed. A small amount 
of steam may also be detected emanating 
from local moist spots, but this is mainly due 
to the vaporization of ground water. In the 
investigation of this heated mass samples were 
taken,. and these were tested qualitatively for 
sulphuric acid and for sulphates of calcium, 
aluminium and magnesium. The tests were 
made by Mr. Jacobs, of the Hospital Labora- 
tory Staff at Ancon, and they revealed the 
presence of all of the above substances, both 
in the shale andeas the white coating on the 
moist spots and steam vents of the mass. 
The yellow deposit near the larger vents is 
sulphur. Sulphuric acid, especially, was 
shown to be present in considerable quantity. 
The origin of the sulphuric acid here was at 
first a puzzle, because the examination of 
many samples, with the naked eye and with 
the microscope, failed to reveal the presence 
of pyrite. Finally samples of eight to ten 
pounds were taken, ground with water in a 
large mortar for some minutes, and then con- 
centrated to a few ounces by washing or 
“panning.” This concentrate showed a high 
content of pyrite, much of which could 
scarcely be seen with the naked eye. Under 
the microscope very small crystals of pyrite 
were noted; also considerable magnetite, pres- 
ent as black sand, and some sub-angular to 
fairly rounded grains of quartz. 
The mainspring of the action here then, as 
in the other instances observed, has undoubt- 
edly been the oxidation of the pyrite. The 
reasons why this oxidation has been so rapid 
and effective, seems to be as follows: 
(a) The finely divided, almost microscopic, 
character of the pyrite gives maximum sur- 
face exposure to atmospheric agencies and 
greatly promotes oxidation. 
(b) The very warm, moist atmosphere. The 
tropical sun shining directly on dark rock 
surfaces produces a temperature sufficiently 
SCIENCE 
[N.S. Vou. XXXV. No. 905 
high to greatly promote oxidation, especially 
in the presence of slight moisture. 
(c) Once oxidation of the pyrite has been 
started the heat thus generated tends to ac- 
celerate chemical action and thus the heating 
increases in geometric progression. 
(d) When the heat of pyrite oxidation 
reaches the comparatively low temperature of 
oxidation of the hydrocarbons present in the 
lignitic shale, they, too, become oxidized and 
still further add to the temperature. Finally 
the fixed carbon content tends to become oxi- 
dized, at least in part, and gives maximum 
intensity to the action. 
(e) Some heat is also generated by the ac- 
tion of the free sulphuric acid on the calcium 
carbonate for the formation of gypsum. 
Other minor chemical actions added their 
quota to the total heat. 
As the temperature rises all chemical activ- 
ity is vastly stimulated and the heating in- 
creases to a maximum. After the most read- 
ily oxidizable substances are consumed the 
heat gradually dies down toward normal tem- 
peratures, which may be reached in a few 
weeks or months. The intensity and duration 
of the heat depends largely upon the percent- 
age of finely divided pyrite, volatile matter 
and fixed carbon in the rocks. 
Some of the geological considerations sug- 
gested by a study of this phenomenon are: 
(a) Chemico-thermal springs. Whenever 
jointing fissuring or change of groundwater 
level gives free access of oxygen-bearing sur- 
face waters to beds which contain the neces- 
sary finely divided pyrite, and carbonaceous 
matter, a heating up of such beds is likely to 
result. Groundwater flowing over such 
heated beds, and coming to the surface in the 
general vicinity of them, would constitute 
thermal springs. 
(b) Should a rise of land surface bring py- 
rite-bearing beds from subaqueous to terres- 
trial conditions, oxidation of the pyrite might, 
in the course of a year, give local redbeds that 
would otherwise require centuries of atmos- 
pherice action to produce. Of course it is rec- 
ognized that no very extensive redbeds could 
be produced in this way. 
