90 PROCEEDINGS OE THE WASHINGTON MEETING 



overthrust blocks, one limb of anticline or syncline, an appressed fold, a series 

 of appressed folds, or a local, single flexure in a pile of otherwise horizontal 

 beds. In many an instance the observer is long delayed in reaching a con- 

 clusion as to which of these or other categories a group of inclined beds is to 

 be finally referred ; after years of research he may not be able to make this 

 decision. Yet in his field notes and reconnaissance report, if not in his final 

 publication, he should have a broad term by which to refer to the structural 

 unit here described. . 



Feeling this need during years of reconnaissance and detailed studies in the 

 Canadian Cordillera and elsewhere, the writer has suggested the name "homo- 

 cline" to cover the case. 1 A "homocline" is thus "any block or mass of bedded 

 rocks all dipping in the same direction." According to one of its several 

 definitions, "monocline" has exactly the-meaning given to "homocline," and it 

 is necessary to show reason for preferring the new term. 



Different Definitions of "Monocline" 



"Monoclinal" was invented by W. B. and H. D. Rogers, who wrote: "We 

 propose the term monoclinal to signify a sameness in the direction of dip, and 

 shall term a mountain or valley in which such sameness prevails a monoclinal 

 mountain, or monoclinal valley." 2 Since sameness of dip, rather than the 

 singleness of dip direction, is emphasized, it appears that "homoclinal" would 

 have been etymologic-ally preferable. Though the originators of the word, W. B. 

 and H. D. Rogers made very little use of it, and then almost, if not quite, ex- 

 clusively in the adjective form. Some authors have since employed "mono- 

 clinal" as a noun, equivalent to the proposed "homocline," signifying merely 

 a series of beds dipping in the same direction ; but "monocline" in this sense 

 has been comparatively little used. 



In 1865 Page used "monoclinal" as a noun, meaning a one-limb flexure, or 

 the same as "monoclinal fold," Powell's name for well known flexures of the 

 Colorado plateaus. 3 In 1880 Dutton adopted this usage. 4 In 1882 Dutton used 

 "monocline" with the same meaning, and also in 1882 A. Geikie published what 

 seems to be the first formal definition of "monocline." He expressed it in the 

 following words : 



"Curvature occasionally shows itself among horizontal or gently inclined 

 strata in the form of an abrupt inclination, and then an immediate resumption 

 of the previous flat or gently sloping character. The strata are thus bent up 

 and continue on the other side of the fold at a higher level. Such bends are 

 called monoclines, or monoclinal folds, because they present only one fold or 

 one-half of a fold, instead of the two in an arch or trough." 5 



The Dutton-Geikie usage represents a considerable narrowing of meaning 

 when compared with the "monocline" implied in the Rogers' use of the ad- 

 jective "monoclinal." The same narrower definition of "monocline" is to be 



1 R. A. Daly : Memoir 68, Geol. Survey of Canada, 1915, p. 53. 



2 W. B. and H. D. Rogers : Reports of the Association of American Geologists and 

 Naturalists, 1840-1842, Boston, 1843, p. 4S5. 



3 D. Page : Handbook of Geological Terms, Edinburgh and London, 1865, p. 312. 



J. W. Powell : Colorado River of the West, Washington, 1875, fig. 67, opp. p. 183. 



4 C. E. Dutton : Report on the geology of the high plateaus of Utah, 1880, p. 26. 



5 A. Geikie : Textbook of Geology. London, 1882, p. 515. 



