34 
of some kind. It is a variety of ‘‘phonolite.” The 
writer does not believe that the two eruptives described 
have any bearing on the origin of the gold of this 
origin. Fire tests on the ‘‘phonolite” failed to reveal a 
trace of gold, and, as yet, no ‘‘pay mines’ have been 
found in close proximity to the Black Dyke. The 
evidence all seems to point to the granite as the source 
from which the gold and other vein minerals were 
derived. Micas have been found by the work of 
Sandberger and others to contain nearly all the heavy 
metals (according to Phillips, gold, tellurium and mer- 
cury, ‘‘from want of the necessary appliances were not 
sought for” by Sandberger); and it would not be un- 
reasonable to expect that future researches may reveal 
traces of gold in some of the micas of this region. If 
this prove to be the case, it would not be difficult to 
form some conception of the manner in which the dif- 
ferent changes, which made up the evolution of great 
gold veins from granite beds, took place. This paper 
has attempted to convey some idea of the tremendous 
alteration and working-over by aqueous agencies, to 
which the rocks of this region have been subjected. If 
there is an analogy between this alteration and the 
occurrence of the gold, the degree of alteration would 
satisfactorily account for the great richness of the de- 
posits, and afford much promise of permanence and 
value at great depths. The bands or zones of altera- 
tion were caused by the action of underground waters. 
There is no reason to believe that these waters were of 
a very high temperature, but that they were hotter than 
ordinary surface waters is undoubted. Subterranean 
waters are waters from the surface which have descended 
through cracks or by percolation through the 
porous rocks. As stated by Presturch, ‘‘the higher 
temperature of the waters at great depths 
would give rise to convection currents which 
establish a constant removal of the mineral 
matter in solution from deep-seated sources.” The 
meeting of hot waters from below, charged with solid 
contents derived from the rocks, with surface waters, 
would reduce the temperature of the ascending waters ; 
and the precipitating agents brought down by surface 
waters would bring about the deposition of the mineral 
matter in the interstitial spaces left by the removal of 
the matter originally therein. The process would thus 
be a constant interchange of matter—abstraction and 
replacement. In this way if minerals or rocks of a dif- 
ferent character from those existing near the surface 
were met with and acted upon by these waters great 
changes could be produced ; but, if the rocks were prac- 
tically the same to great depths, as is likely the case 
in this region, the alteration produced would be simply 
changes in the texture of the rock, and in the propor- 
tions of the different constituents. These molecular 
changes would afford opportunities for the segregation 
and concentration of minerals, and would account for 
the concretionary veins of quartz and feldspar, hereto- 
fore described, as well as the zones or belts impregnated 
with auriferous pyrites. The micas of the granites 
would be acted upon; the iron and gold contained in 
the mica (if the mica held gold) changed into sulphates 
in solution, which were in turn reduced by the organic 
matter brought down by waters from the surface, to 
metallic sulphides (or the iron to a sulphide holding the 
gold in a finely divided metallic state), and deposited in 
the pores of rock already rendered porous as described 
above. 
Accounting for the derivation of the sulphur neces- 
sary for the formation of sulphates is the one link miss- 
ing in the chain of reasoning which makes up the theory 
of ‘‘lateral secretion.” The votaries of the ‘‘ascen- 
SCIENCE. 
[Vol. XXIII. No. 572 
sion” and ‘“‘sublimation ” hypotheses hold that the sul- 
phur must come from deep-seated sources, but they do 
not satisfactorily explain why it should be present at 
depth and not in the rocks a few thousand feet above. 
Neither do they tell us whence comes the sulphur in the 
great sulphide lead, zinc and copper ores of the upper 
Mississippi lead region. There the ore occurs in cham- 
ber deposits or flats in unaltered Silurian limestones; 
no eruptives of any kind are met with; and, so far as 
known, no fissures or other connections have existed, or 
do exist between these beds and the rocks underlying 
them at depth. 
The atmosphere seems to have been, so far as the 
writer knows, not considered as a possible source from 
which the sulphur required for these reactions may have 
been derived. The carbon necessary for the formation 
of coal was derived from the atmosphere, and most 
geologists hold that the air must have contained a larger 
amount of carbonic acid at the beginning of the Carbon- 
iferous period:than at the present time. Much sulphur 
is often present in coal. Is it unreasonable to conjec- 
ture that, during those early periods, the air contained 
gases which are no longer present, or only present in 
infinitessimal quantities? Great difficulty has always at- 
tended analyses of air, but the examination of rain water 
has thrown much light on the impurities contained in 
the atmosphere. Geikie says: ‘‘Nitric acid some- 
times occurs in marked proportions—sulphuric acid 
likewise occurs, especially in the rain of towns and 
manufacturing districts. Sulphates of the alkalies and 
alkaline earths have been detected in rain.” He attrib- 
utes the disintegration of mortar in walls to the action 
of nitric and sulphuric acids of the air and says: ‘‘The 
mortar of walls may often be observed to be slowly 
swelling out and dropping off, owing to the conversion 
of the lime into sulphate.” The Colorado Front Range 
is believed by geologists to have been raised above the 
sea, asa long, narrow, northerly and southerly island, at 
about the close of the Archean era; but not upheaved, 
into a great mountain range, until the close of the- 
Mesozoic. There was thus ample time for the slowest 
kinds of chemical and molecular changes to take place 
in. Atmospheric erosion, during these countless cen- 
turies, must have carried away several thousand feet of 
the top beds. To make up for this waste, it is proba- 
ble that the land was at times upraised to some extent. 
These sporadic upliftings would likely be accompanied 
by more or less disturbance of the strata; fissures would 
be produced, in the areas of greatest disturbance, which 
would form channels for the circulation of waters; and 
thus aid in the alteration of the country rock into the 
bands or zones heretofore described. It was during this 
period that the sulphur was probably introduced. 
Whether it was derived from the air and brought down 
by surface waters, or from the seas bordering this long 
island, through infiltration, or introduced trom below 
in some manner, is as yet an unsolved problem. In the 
formation of these belts of alteration and auriferous 
pytites ‘‘fahlbands” was the first stage in the genesis of 
these gold deposits; and ‘“‘lateral secretion,” aided. by 
“ascension,” which is a necessary adjunct to the circula- 
tion of underground waters, seems to account for the 
first stage, as well as for the more recent one of con- 
centration into veins rich enough to work. At the close 
of Mesozoic time this long, narrow island, which had, 
for untold ages, existed as land, was thrown up into a 
mountain range. It was during the folding and con- 
tortion of these rocks, attending their upheaval, that 
the fissures, since filled with auriferous quartz, were 
probably formed. Enormous lateral pressure caused 
these great peaks and anticlinal ridges. A torsional 
