May 21, 1920] 



SCIENCE 



519 



1919, the production of natural gas in that state 

 decreased 20 per cent. 



Some characteristics of tlie Balcones fault zone 

 in Bexar county, Texas: E. H. Sellakds. The 

 Balcones fault zone lies at the inner margin of 

 the Coastal Plains of Texas, and the scarp result 

 ing from the faults is a conspicuous topogi'aphie 

 feature whieli in several counties separates the 

 coastal plains from the high plains of the interior. 

 The fault scarp is most pronounced in Uvalde, 

 Medina, Bexar, Comal, Hayes and Travis counties. 

 The formations observed to have been affected by 

 these faults are those of the Lower and Upper Cre 

 taceous and Eocene, while the Pleistocene forma- 

 tions have not been observed to be affected by 

 faulting. Hence the age of the faults may be be- 

 tween Eocene and the Pleistocene. The numfber 

 of faults within the fault zone as developed in 

 Bexar county can scarcely be estimated. A few 

 are seen at the surface; a number of others are 

 located by well records, but with little doubt there 

 are many more faults than have been located by 

 either of these methods. They are normal faults 

 with the downthrow to the south in most cases. 

 The faulting is accompanied in some places by 

 gentle folding, and the small oil fields of this 

 county are found apparently upon structurally 

 high areas produced by a combination of faulting 

 and more or less folding. The width of the zone 

 of faulting approximates 25 miles, and yet it re- 

 mafins to be determined how much farther to the 

 south or southeast faulting in this zone may be de- 

 tected. 



The OzarHan of Missouri: E. B. Bkanson. 



The nature of Beatricea undulata: W. H. 

 Shidelee. 



The possiiility of a relationship ietween crystal 

 types and the mode of occurrence of minerals: W. 

 A. Take. Along with other lines of research on 

 the origin of crystals, the question arises as to 

 whether the mode of occurrence shows an influence 

 upon the type in which a given mineral crystallizes. 

 If physical conditions influence the molecular ar- 

 rangement this should be the ease. A study of 

 ISiS common minerals, classified into eight zones 

 shows that there is only a very general influence. 

 The influence of composition appears to be more 

 marked. The higher classes of symmetry are the 

 most abundant in certain zones, yet physical fac- 

 tors do not appear to control the class of symmetry 

 of a mineral. In large groups the physical condi- 

 tions appear to be a factor but it is questioned 

 whether the chemical factors are not of vastly more 

 importance in these same zones. 



An analysis of the process of thrust-faulting: 

 T. T. QuiRKE. It is probaible that there is so sharp 

 a zone of division between the surficial plastieo- 

 frangible crust and the interior plastico-rigid mass 

 that the part subject to rupture may be considered 

 a separate member even though flow deformation 

 may extend beneath it. Earth stresses due to the 

 adjustment of a plastico-frangible crust to a sihrink- 

 ing interior affect members as wide as the conti- 

 nents and oceans are broad. These members fail 

 near the ends under a stress which is rotational and 

 unequally transmitted throughout the length of 

 each member. The members fail after flexure 

 somewhat in the manner of long columns. This 

 type of rupture combined with a rotational stress 

 makes a strong tendency to rupture at angles low 

 at depth and high near the surface. Immediately 

 after rupture a geologic process of abrasion comes 

 into play. Abrasion is greatest where friction is 

 most intense, at the steep parts of the fault plane. 

 This movement of millions of tons of rock passing 

 several miles along the fault plane will abrade the 

 steep part of the plane to a lower angle and pro- 

 ject to the surface the original low angle break. 

 From which it follows that there may be a relation 

 between the steepness of angle and the amount of 

 displacement after rupture. 



The mechanical interpretation of joints: Walter 

 H. BuCHER. On Mine Fork, Magoffin county, Ky., 

 at the crest of an anticline in the upper third of 

 a thick sandstone formation exposed in nearly ver- 

 tical cliffs, two systems of joints are seen inter- 

 secting at an angle of approximately 120°, which 

 is bisected by the horizontal direction. In this 

 case, undoubtedly the joint planes, representing 

 planes of shearing, were formed by simple tension 

 and were arranged in such a way as to have the 

 direction of maximum tension bisect the obtuse 

 angle. In 1896 the French engineer Hartmann 

 published the results of extended experimentation 

 on the planes of shearing in metals, in which he 

 found that the angle formed by the yield planes 

 differs the more from 90° the harder and the more 

 brittle the material is, and that the direction of 

 maximum tension bisects the obtuse angle while 

 that of minimum tension (generally negative, i. e., 

 compression) bisects the acute angle. O. Mohr, 

 in 1900, gave a mathematical theory to account for 

 this behavior. The author demonstrated the use- 

 fulness of this relation in interpreting the stress 

 conditions underlying the fracturing of materials 

 in well-known tension, compression and torsion 

 tests. He then proceeded to apply this method to 

 a number of joint systems taken partly from liter- 



