F. W. Mar — So-called Perqf shite from Arkansas. 403 



the river. There is every indication however of a very modern 

 elevation (40± feet) of the region, accompanied by a rapid 

 deepening of the main channels of drainage, in the fact that 

 these tributaries have but recently begun eroding their beds 

 near their mouths. This process has in no case extended more 

 than one fourth mile. In thus eroding their beds the streams 

 in many cases have deepened their channels in lines which do 

 not correspond with their buried channels but lie to one side 

 or the other ; and so we find them running over ledges of rock 

 near their mouths, which has led many observers to the conclu- 

 sion that the tributaries could not flow over buried channels. 

 In all cases that I have examined, however, I have found 

 strong evidence of the existence of such channels — of which 

 there is positive proof in many wells and excavations. 

 Beaver Falls, Pa., August 9, 1890. 



Aet. LI I. — On the so-called Per of shite from Magnet Cove, 

 Arkansas ; by F. W. Mar. 



In 1877, it was shown by Knop ; * that the supposed perof- 

 skite of the Kaiserstuhl, contained besides titanium a consider- 

 able amount (23 p. c.) of niobium and tantalum, and he accord- 

 ingly made it an independent species and named it very appro- 

 priately Dysanalyte. The analysis of the similar mineral from 

 Magnet Cove, Arkansas, the results of which are given below, 

 shows that it is also distinct from perof skite and is to be classed 

 with dysanalyte. For the material for analysis I am indebted 

 to the kindness of Professor E. S. Dana. 



The method of analysis was as follows : - 500 gram, of the 

 carefully selected mineral were placed with about 1 5cm 3 of con- 

 centrated sulphuric acid in a platinum crucible of 150cm 3 capa- 

 city and, the whole being covered with a watch-glass that the 

 progress of the decomposition might be easily observed, boiled 

 for ten or fifteen minutes. The cooled product was poured 

 into 600 or 700 cm 3 of cold water and allowed to stand over 

 night or until the calcium sulphate was completely dissolved. 

 A small residue was usually found and this was put through 

 the same process. Any final residue is silica and sometimes 

 a little tantalum or niobium oxide. The former was deter- 

 mined by evaporation with sulphuric and hydrofluoric acids 

 and the remaining oxide was added to the main oxides. 



* Zeitschr. fur Krvst, i, 284, 1877. 



