710 



SCIENCE 



[N. S. Vol. XXXVII. No. 958 



witli cosmogenetic problems, ought to be 

 designated by a different term. The need of 

 such a term, has long ago prompted its adop- 

 tion, as will be evident from the following 

 quotations from various text-books and geo- 

 logical papers, selected somewhat at random. 

 " Manual of Geology," Dana, 4th ed., p. 366 : 



The ridges of the Great Basin . . . have been 

 assumed to be each limited by faults . . . and to 

 have become, in effect, monoelinal orographie 

 'bloclcs.^ 



" Elements of Geology," LeConte, 5th ed., p. 

 239: 



The strata are broken into prismatic blocks. . . . 

 The slipping of these hlocTcs has given rise to 

 cliffs. 



" An Introduction to Geology," Scott, 2d ed., 

 p. 5: 



Eocks are divided into still larger masses or 

 hlocks by . . . fissures and planes of dislocation, 

 or faults. 



(Pp. 464 and 465) : The plateau of basalt has 

 been fractured into a series of Uocks which are 

 tilted. . . . 



" Exploration of the Colorado Eiver of the 

 West, and Its Tributaries," Powell, p. 

 184: 



The faults . . . divide the district under con- 

 sideration into long belts or blocks. ... In ex- 

 amining the downthrow of these blocTcs, it is 

 observed. . . . 



" Geology of the Henry Mountains," G. K. 

 Gilbert, p. 23: 



The strata of the upper part of the arch (of 

 Mt. Ellsworth) are divided (by faults) into a 

 number of prismoid blocTcs. 



" The Geology of the Eastern Portion of the 



Uinta Mountains," by J. W." Powell, pp. 



16, 17: 



When the Modes into which a district of country 



has been broken by faults are greatly tilted . . . 



the uplifted edges of such hloclcs often form 



long mountain ridges. ... In this region many 



zones are found to be divided into small Modes by 



faults. . . . Fig; 4 is a bird's-eye view of the Modes 



mentioned. . . . Fig. 5 is a diagram of the same 



region showing the Modes into which it is severed. 



^ Italics here and below by the writer of this 

 note. 



. . . Many other areas far more complex than these 

 have been discovered where a zone has been broken 

 into blades and these blodcs tipped and con- 

 torted. . . . 



" The Ore Deposits of New Mexico," Lind- 



gren, Graton and Gordon, Professional 



Paper 68, U. S. Geological Survey, p. 25 : 



The principal disturbances . . . are marked by 



a series of . . . ranges of apparently tilted Modes. 



Bulletin of the University of Texas, No. 93; 



" A Sketch of the Geology of the Cliisos 



Country," p. 80 : 

 It (the Chisos country) covers a part of a 

 sunken Mode, which measures about 39 miles from 

 east to west and which has settled from four to 

 six thousand feet below the level of the terranes 

 on either side. 



Science, N. S., Vol. XXXVII., No. 945, p. 

 226: 

 Keyes speaks of the "so-called fault-6!offc 

 mountains ' ' and refers to a statement by Spur 

 that no one has ever seen the fault-lines Modeing 

 out the desert ranges. 



It will be seen from these quotations that 

 hloch is a term which has long been in use, 

 and which is being used at the present time 

 with a definite meaning, similar to that pro- 

 posed. It seems to be needed. If retained 

 and used in the same sense as heretofore, it 

 will aid in giving greater precision to the 

 geological nomenclature. We need the term 

 segment for a slightly different use, as already 

 stated. 



J. A. Udden 



UNrvERsiTY OP Texas 



CRITICAL CRITERIA ON BASIN RANGE STRUCTURE 



Charles E. Keyes in a recent number of 

 Science' presents a note entitled as above in 

 which he expresses in general terms his lack 

 of belief in " Basin Range Structure," so 

 called, and suggests deilative agencies rather 

 than local tectonic displacement as the im- 

 portant factor in the formation of such ranges. 



The writer has no desire at this time to de- 

 fend the hypothesis of basin range structure, 

 though he is thoroughly convinced of the 



'N. S., Vol. 37, No. 945, p. 226. 



