lieci'ew of Recent GeoUxjical Literature. 117 
in this spring water, on the supposition that its main sovu'ce is the same 
as that yielding the waters of the other groups. 
3. The presence of so large quantities of the bicarbonates of calcium 
and magnesium points to a prolonged contact of the waters with the 
limestones. 
4. The almost total absence of iron salts indicates either a source 
quite free from ferruginous minerals, or more probably the oxidation 
of dissolved iron and its previous precipitation. 
5. The high percentage of chlorides may be derived from the Silurian 
rocks or with less probability from the more distant Jura-Triassic beds. 
6. The large percentage of sodium bicarbonate probably indicates an 
origin among silicate rocks, whence the soda (and potash) may come as 
carbonates formed by the decomposition of the rocks by atmospheric 
waters containing carbonic acid, or as alkaline silicates, which react 
upon the limestones (calcium carbonate) before reaching the surface. 
7. The sulphates may come fi"om unseen gypsum beds, but it is prob- 
able that they come in greater part, at least, from the oxidation of sul- 
phides in granites, igneous rocks, or even sedimentary beds. 
8. The concentration of the solutions -that is, the large quantity of 
mineral matters contained in the springs' waters, comes evidently from 
prolonged contact with rocks, such as would arise from percolation and 
probably also from an increased solvent power of the water, due to heat 
or pressure, or both combined. 
9. The difference in temperature of the several springs is remarkable 
as showing that either the waters come from different sources, or if 
coming from the same source have been cooled in an unequal degree by 
passing through diverse strata, or through the influx of cooler foreign 
waters. 
10. The variation of the springs between summer and winter, in their 
contents of minei-al matters dissolved, in the quantity of water flowing 
from them and in the volume of gas yielded, together with the remark- 
able uniformity of temperature throughout the year in some of them, 
are evidently significant phenomena. 
The gas with which the water is charged is carbon-dioxide and the 
author reviews the various explanations usually offered for its origin. 
It is believed that in this instance the gas is derived from the chemical 
decomposition of limestone by acid waters or salts. The theory ad- 
vanced for the origin of the natural gas at Manitou is thus summarized: 
"Water percolating through silicate rocks and Ijecoming highly miner- 
alized under favorable conditions of temperature and pressure, makes 
its way through cracks and profound rock-fissures by the action of 
gravity and the ascensional power imparted by heat, to the limestones 
west and north of Manitou. It is here increasad in volume and in dis- 
solved salts Vjy the numerous additions of seepage waters from the local 
rocks, and also lowered in temperature at the paints where these in- 
fluxes occur. By chemical reactions some of the dissolved salts are 
changed, and the carbon-dioxide originally held (almost entirely) by the 
limestones is liberated from that combinaticm hut dissolved in the water 
