FOLDS AND FAULTS. 235 



on the extreme west, forming the easternmost range of the Rocky moun- 

 tains. The trend of the axis is southeastward. 



It is a significant fact that the axes of all five of the great folds when 

 prolonged strike approximately the same point in the Gulf of Mexico, 

 a short distance from the mouth of the Mississippi river, a place where 

 a maximum load of sediments h'om the North American continent is 

 now being deposited ; or, in other words, the axes radiate from this 

 point. 



Comparatively simple in its general geologic structure, easy of subdi- 

 vision into tolerably Avell-defined minor groups according to lithologic 

 features, and abundantly supplied with characteristic fossils in all its 

 beds, the Paleozoic series of the interior basin still possesses stratigraphic 

 phases highly complicated in their nature. It is an arrangement of strata 

 such as might occur along the coast of any continental mass receiving 

 sediments from numerous sources and forming very distinct interlocking 

 beds, each of which rapidly or gradually thins out in all directions and 

 is r€])laced by others. It is an arrangement which presents great diffi- 

 culties to a natural geologic classification of the beds that would be appli- 

 cable to all portions of the district, both on account of the vastness of the 

 province and the multiplicity of conditions under which the depositions 

 were made. 



Minor Corrugations. — Besides the flexures just mentioned, there are in 

 the region many smaller folds and synclines, which have a trend inde- 

 pendent of the larger ones. These are usually grouj^ed into series of 

 more or less limited extent, the different series being independent of 

 one another. Their existence has long been known, yet the extent and 

 amplitude of none have been determined with accuracy. In Iowa a 

 number of low folds have been recognized. Their axes have a northwest- 

 southeast direction in the eastern part and northeast-southwest in the 

 western portion of the state. Several have also been made out in central 

 Iowa. In the neighboring states similar small folds have been noted 

 from time to time. 



Faults. 



Alleged Faulting. — In the early days of geologic exploration in the Mis- 

 sissippi valley, faults, many of considerable extant, were frequently re- 

 ported at different places. In his canoe voyage up the Des Moines river 

 from its mouth to the Lizard fork, near the present site of Fort Dodge, 

 Owen recorded a number of very marked instances. Worthen, who made 

 the same trip a decade later, also claimed to have recognized some very 

 striking dislocations of the strata. Subsequent investigations haA^e not 

 only failed to substantiate the earlier observations, but have proved con- 



