Willis and Hayes — Appalachian Faulting, etc. 257 



cyrtolite (in infinitely fine crystals) and also other silicates of 

 the rare earths. The U0 2 found by Eakins, like the U0 3 

 found by Blomstrand in the Xaresto xenotime, is probably to 

 be regarded as an isomorphous replacement of thoria. The 

 green color would seem to indicate that the U0 2 was present 

 as a phosphate. The Th0 2 is not constant even in the same 

 locality, for some of the common xenotime from this same 

 region, tested for thoria alone proved to contain over four 

 per cent.* Another trial on new material gave 2*36 per cent 

 Th0 2 . The fluorine, it will be noticed, is richest in the 

 brown variety (only a mere trace in the green) which is also 

 the most hydrated and richest also in alumina and ferric iron. 

 Prof. Henry A. Rowland, of the Johns Hopkins University, 

 examined spectrographically some of this Brindletown xeno- 

 time, several years ago, and reported it to be uncommonly rich 

 in scandium ; even more so than the South Carolina polycrase. 



Aet. XXXIX. — Conditions of Appalachian Faulting / by 

 Bailey Willis and C. Willard Hayes, Appalachian 

 Division IT. S. Geological Survey. 



[Published by permission of the Director.] 



Chamberlin in 1882 suggested that folding and faulting of 

 strata in narrow zones of great sedimentation might be due to 

 the mechanical condition produced in deeply buried layers, 

 which would be bent initially beneath the mass laid upon 

 them before compression produced greater deformation.f 

 Geologists of the Appalachian division of the U. S. Geolog- 

 ical Survey, approaching the problems of structural geology 

 through field study in the belt from Pennsylvania to Alabama 

 and experiments on stratified blocks, which were compressed 

 under shot, were led independently to the conclusion that 

 the condition which determined folding and faulting re- 

 sided in the strata folded or faulted and was a mechanical con- 

 dition determined by the frangibility, flexibility or plasticity 

 of the strata and by their attitude as struts toward pressure. 

 The experimental work and some observed facts bearing on 

 the conclusions are described in an article now in press,;f and 



* As the thoria was separated by repeated hyposulphite treatments in a neutral 

 HC1 solution and precipitated finally as oxalate and as the ignited oxide was pure 

 white, there can be no doubt of its identity. 



\ Geology of Wisconsin, vol. 1, p. 76. 



X Mechanics of Appalachian Structure. Bailey Willis, X filth Ann. Report U. 

 S. G. S. 



Am. Jour Sci.— Third Series, Vol. XLYI, No. 274— October, 1893. 



18 



