CENTURY OP IOWA GEOLOGY 429 



continuous bed of mineral fuel but for a stratigraphic level where 

 workable coal is to be especially sought for in a wide belt fringing 

 a great basin. 



CONTINENTAL TERRANAL CORRELATION BY OROTAXIS 



What continues today to bother the geologist more perhaps than 

 any other subject relating to earth knowledge is the problem of 

 exact stratigraphic correlation. It is, indeed, a phase of geology 

 which has been a source of embarrassment ever since the science's 

 birth two centuries ago. When, during the last quarter of the 

 last century, stratigraphy began to demand quantitative rather than 

 qualitative results other stratal criteria had to be found which in the 

 field are of even greater practical value than could be hoped for 

 with the fossils. When comparisons are made with other criteria 

 the shortcomings of the paleontologic methods become glaringly 

 unsatisfactory. Closely examined the paleontologic scheme of geo- 

 logic classification is found to be not an arrangement of terranes 

 at all, nor a logical table of historic events, but merely a rather im- 

 perfect grouping of faunas. The question arises whether in 

 stratigraphy we should not be better off today if we were to ignore 

 the fossils altogether, or recognize them only in a general way. 



As originally defined"*' orotaxis, or stratigraphic classification 

 upon the basis of diastatic or diastrophic movements is essentially as 

 follows : Immediate cause for the changes which take place in the 

 relations of the land and the sea areas is is to be sought in orogenic 

 and epeirogenic movements. Since, however, the two kinds of 

 crustal oscillation cannot be readily distinguished practically, and 

 as it is of small advantage to separate them theoretically, the 

 structural results produced may be regarded as arising from the 

 same cause — that is, from mountain-making forces. The greatest 

 and most abrupt modifications in sedimentation, and consequently 

 in lithologic, faunal and, in fact, all characters, are those con- 

 nected directly with diastatic activity, producing depression of some 

 areas and the uprising of others. Geologic chronology is believed, 

 therefore, to find true and rational basis in tlfose changes which 

 primarily control sedimentation, and which are intimately con- 

 nected with the genesis of mountains. It is proposed to emphasize 

 this feature as fundamental by marking out the leading sub- 

 divisions of geologic time and to define general stratigraphic succes- 

 sion in accordance with the cycles of orogenic development, calling 

 the classification a systematic arrangement of mountains, or orotaxis. 



=»American Geologist, Vol. XVIII, pp. 289-303, 1896. 



