Record op Geology of Texas, 1887 - 1896 . 
247 
Tarr, Ralph S. 
tbeniselves in explanation of this phenomenon, wliich is quite remarkable 
in a river with a fall of from two to three feet per mile. Since the Col- 
orado is a superimposed river, flowing in its present course chiefly by 
accident, dt is possible that before the Quaternary uplift the river may 
have been sufficiently old, in this part of its valley, to have the serpentine 
course common to sucli rivers. Thus, the present form of the valley may 
be inherited from that time. Another possible cause is that the slow 
removal of the Silurian by retarding the down-cutting in this part of the 
river-channel has induced a temporary old age condition.'’ 
Attempt of the Colorado to readjust itself to new conditions. The evi- 
dence. Another unexplained phenomenon is that the divide between the 
Colorado and the Brazos is close to the latter and far from the former. 
‘Tt is probable that both the Brazos and the Colorado originated under 
ipractieally the same conditions ; that is, upon the new Cretaceous land 
elevated above the sea during the great Tertiary mountain uplift. Their 
course was plainly chosen with reference to conditions appearing on the 
surface then existing without regard to what lay below. lAfter cutting 
through the soft, nearly horizontal Cretaceous rooks, the Colorado came 
upon the buried Paleozoic and encountered not only the iCarboniferous 
for a considerable distance, but also the much harder Silurian with which 
it has long been struggling. Tlie Brazos, on the other hand, by the acci- 
dental choice of a more easterly course, avoided these difficulties. ”■ 
The coinsequence of this difference between the two rivers is that while the 
Colorado in Mills county flows at an elevation of 1,200 feet above the 
sea level, the Brazos, in the same latitude, has cut down to within COO 
feet of the sea level in its soft bed. 
“This fact has given the Brazos a great advantage over its competitor, 
the Colorado, for drainage territory; and this, in the battle for conquest 
of headwater drainage area, has enabled the Brazos to push the divide 
close up to the Colorado in territory, which, under more favorable cir- 
cumstance, should belong to the latter stream.” 
396. 
The Permian of Texas. 
Amer. Jour. Science, III, Vol. XLIII, pp. 9-12. Xew Haven, 
Jan., 1892. 
The existence of Permian in Texas reported by various observers. Con- 
clusive evidence furnished by Professor C. A. White (Am. Nat., Vol. 
XXIII, p. 109). Pacts furnished by Mr. W. F. Cummins (1st and 2nd 
Repts. Oeol. Surv. of Texas), who estimates that Permian strata have a 
thickness of full}^ 5,000 feet. “The Permian of Texas occupies a broad, 
gentle syncline in the Carboniferous, the western arm being a part of the 
’Rocky Mountain uplift. Its present boundaries, and consequently its 
former extension, have not been ascertained. Many hundred square miles 
are covered by these strata in the sub-humid and ai-id belt of Central Texas, 
the Pecos river forming approximately the western boundary, while on 
the east the strata do not extend much farther than Abilene,” P. 9. 
