Geology of Ft. Apache Region, Ariz. — Reagan. 285 
spring. Each of the deposits reaches a great thickness, the 
Elsesa being 250 feet in thickness. The springs were cold as 
is indicated by the gastropod shells incased in the travertine. 
The finding of these shells also seems to indicate that the wa- 
ters of the springs were more or less laked. Besides the shells, 
beetles and other insects were found. In these deposits are 
to be found trees as large as the pines of today. 
RESUME. 
The Archaean strata had been deposited, plicated, raised 
above the water, and eroded, before the age of the Algonkian. 
In that age a coast-line slowly encroached upon the Archaean 
area, paring its ridges, filling its hollows, first, with the coarse 
siliceous detritus of the advancing beach ; secondly, with the 
finer mud spread by the currents and waves in the shoal-waters 
that progressively followed the beach ; and, thirdly, with the 
limestone that was slowly formed in the waters remote from the 
shore line. Associated with this advance of the beach-line and 
the deposition of sediments were great volcanic disturbances, 
the lava flows of which are interstratified with the elastics. 
Most of the lavas then out-poured are of the dioryte, and dia- 
base types. When the shore-line had advanced till it nearly or 
quite covered the Archaean area, the sea was again removed 
and the erosive agencies set about to reduce the land area to a 
peneplain. Where the shore-line was then we cannot tell, 
neither do we know whether the land area was a small island 
or a continent. This we do know, however, that the time be- 
tween the retreat of the sea and its return was of long duration. 
At last it returned and in it was deposited the Tonto formation 
followed by the upper Silurian ( ?), Devonian, and Lower Red 
Wall group. Then the sea became shallow and the shore ad- 
vanced back and forth across the region time after time, thus 
causing it to be swamp or sea according as the ocean receded 
or advanced. In the swampy periods the Lepidodendrons and 
the Calamariae flourished, and in the sea periods the Produc- 
es cora, Productus semireticulatus, Productus costatus, Spir- 
ifcr cameratus'and Athyris sitbtilita lived. This was the middle 
Coal Measure period. Before its close the sea gained complete 
possession again. This middle coal series or upper \\v<\ Wall 
group, was followed by the Auberv group. Then-there was 
