306 R. /S. Tarr — Topographic Features of Texas. 



mineral seems to be very closely allied to, if not identical with, 

 the polycrase from Hitteroe, Norway, analyzed by Eammels- 

 berg ; in which he found 



Cb 2 & 20-35 



Ta 2 5 _ 4-00 



TiU 2 . 26-59 



Y 2 3 _. 23-32 



Er s O, v.. 7-53 



Ce 2 3 . __ 2-61 



FeO 2-72 



U0 2 7-70 



H 2 4-02 



98-84 



By calculating the above, without knowing the molecular 

 weight of the Y 2 3 group but taking it to be 89*5, we arrive 

 at the following approximate formula : 



Cb 2 5 , 4Ti0 2 , 5RO, 2^H 2 0, 

 or 2Cb 2 5 , 8Ti0 2 , 10RO, 5H 2 0, 



which may also represent our mineral when the metallic acids 

 have been accurately separated and their individual molecular 

 weights definitely ascertained ; this we propose to do as oppor- 

 tunity offers. In conclusion we call attention to the fact that 

 this is the first occurrence of a columbotitanate accredited to 

 an American locality. 



Akt. XXXIX. — Origin of some Topographic Features of 

 Central Texas /* by Ralph S. Take. 



The Central Paleozoic area of Texas is a region of older 

 rocks exposed by the removal of the overlying unconformable 

 Cretaceous. The southern portion of this area has since the 

 very earliest times been the seat of extensive denudation as 

 long as any land area remained above the sea. The Potsdam 

 sandstone perhaps derived its sediment from the still older 

 metamorphic rocks. A conglomerate layer in the Lower Car- 

 boniferous series contains pebbles from the Silurian rocks. 

 The same is true of the conglomerate in the Upper Carbon- 

 iferous ; and the Trinity beds, the lowest of the Cretaceous 

 system, when conglomeritic, contain, in this region, chiefly 

 Silurian pebbles. The Quaternary drift has the same peculi- 

 arity. 



* Published by permission of Mr. E. T. Dumble, State Geologist for Texas. 



