246 
Transactions Texas Academy of Science. 
Tarr, Ealph S. 
la period of limestone deposit in the southwest, but of more sandy beds 
to the northwest, which iseems to point to the presence of afi old dand 
area near there, which is now hidden from view beneath the Cretaceous. 
'The last beds of the Brownwood division indicate a return to shallow 
water conditions, and this is followed by the coal bearing shale beds of 
the Waldrip division, following this is the depositiion of alternating 
clays and limestones, containing much clay and a consequent change in 
fauna. The conditions of this deposit seem to indicate that the then shore 
line was in the Carboniferous, and that the Carboniferous beds previously 
deposited and unconsolidated were in part furnishing sediment for the 
forming strata. The Permian conditions are probably being approached, 
and possibly even at this time the basin of deposit has become a par- 
tially enclosed sea. A gap of unknown extent ensues after the close of 
the Permian until the beginning of the Lower Cretaceous which buried 
the PaleozJoie rocks, now by erosion partially uncovered for study.” Pp. 
152 - 153 . 
395. 
Superimposition of the Drainage in Central Texas. 
Amer. Jour, of Science, III, Vol. XL, pp. 359-362. Xew 
Haven, Xov. 1890. 
“A superimposed river, having selected its course with reference to a 
structure now no longer present, naturallj^ finds itself flowing without 
reference to the nature of the newly discovered beds. Thus it is that the 
Colorado in Central Texas is now busy witli a barrier of hard Silurian 
rock, and thus it is that this river flows with a general course at right 
angles to the strike of the Carboniferous rocks in an opposite direction 
to the dip. 
“Not only the Colorado itself, but all its tributaries, flow without spe- 
cial reference to structural weakness; but the smaller branches take 
advantage of the structural peculiarities, showing, in many cases, that 
they are more recent in origin than the time of removal of the Creta- 
ceous. ‘Moreover, some of the medium-sized streams, which in their upper 
and middle course flow, perhaps on Cretaceous, quite regardless of iCarbon- 
iferous structure, have nearer their mouth partly adjusted themselves to 
the new conditions. The number of strike valleys in the lower course 
of such streams is quite astonishing, since it shows to how great an extent 
drainage is dependent upon structure, and how readily, even under great 
disadvantag'es, streams will make use of such weaknesses. 'In the Carbon- 
iferous this is particularly noticeable in valleys carved in soft clays and 
shale. 
“Everywhere may be seen signs oi attempts at rejuvenation, but it was 
not until lately that 1 was able to see that the Colorado itself shares 
this peculiarity. This river flows with a very serpentine course through 
the iCarboniferous, having a length along the boundary of San Saba 
county of fifty miles, while at the end it is only thirty miles from the 
first point. In oue place it makes a bend six miles long where a cut-off 
would reduce the distance to tvvo miles. Several possible reasons suggest 
