562 IOWA ACADEMY OF SCIENCE Vol. XXV, 191S 



titions of the same layers, rather than a simple succession of 

 strata of prodigious and unreasonable measurement. Theoreti- 

 cally such a sequence is best explained upon the assumption tiiai 

 there is a great anticlinorium with closely appressed and over- 

 • turned folds. With this the recent observations seem strictly 

 to accord. 



This appressed condition of the folds appears to obtain also 

 on the west side of the axis where the Pre-Cambrian Beltian 

 rocks, reported to be 30,000 feet in thickness, have sub-uniform 

 dips. When the Beltian section along the Canadian Pacific 

 railway, on the west slope of the Selkirk ranges, was inspected 

 several years ago, during the Transcontinental Excursions of 

 the Twelfth International Geological Congress, the divergent 

 slants of the metargillites were thus interpreted. This proving 

 to be the case there is represented in the northern Rockies a 

 fan-structure that comparas favorably with that displayed in 

 the Alps made classic by the work of Heim and the other Swiss 

 geologists. 



The notably close folding in the northern section of the Rocky 

 Cordillera contrasts strongly with the open flexures in the south. 

 In Montana and Idaho, for example, the major folds are so 

 widely separated that distinct mountain uplifts appear to rise 

 out of the plains. In Colorado similar conditions prevail. 

 Where the extreme southern end of the Cordillera plunges be- 

 neath the arid plains of the Mexican tableland, in northern New 

 Mexico, the flexing, so gentle as to be reduced to three slight 

 wrinkles, represents the complete anticlinorium. 



The stratigraphy of this still virgin region is not without greai 

 interest. The Paleozoics are enormously developed. Where in 

 Iowa we measure the thicknesses of the formations in tens or 

 hundreds o'f feet, in the northern Rockies we calculate them 

 in thousands. Then beneath the Paleozoic strata come tremen- 

 dous thicknesses O'f Pre-Cambrian beds. The Proterozoic succes- 

 sion is seemingly perfectly conformable with the Paleozoic se- 

 quence, but is separated from the Archeozoic metamorphics by 

 a great unconformity. Both Paleozoic and Archeozoic sections 

 rival in every way the great Paleozoic pile of this region. Of 

 course the fcAv days at my disposal last year and the few days 

 during the past snnnner are far too short a time to work out 

 anything like a satisfactory^ scheme. 



