546 IOWA ACADE:\IY OF SCIENCE Vol. XXV, 1918 



fossils would furnish an exact vertical section and a ready means 

 of paralleling coal-seams and guide-horizons in localities widely 

 separated from one another. As time went on this proved nota- 

 bly unsatisfactory and inconclusive. As a practical metliod of 

 correlation the scheme was long since abandoned. In view of 

 the peculiarities of orig'inal sedimentation and the rapid alterna- 

 tion of lithologic and consequently physical conditions it now 

 appears to be extremely doubtful whether the organic remains 

 of these formations ^^^ll ever prove to be effectual correlative 

 features. This is particular!}^ true of Kansas where the method 

 experienced the severest test. 



"With the complete break-down of the fossils as correlative 

 criteria in Kansas, Missouri and Iowa and in fact throughout 

 the Western Interior coal-field, correlation was largely con- 

 ducted by direct tracing of strata from point to point, until 

 there resulted one of the most complete and precise rock-classi- 

 fications known. In the meanwhile similar detailed field-work 

 in the Eastern Interior coal-basin lagged. Through fortunate 

 preservation of a narrow belt of coal measures by drop-faulting* 

 a part of the w-estern section was traced across the supposed 

 barren area along the line of the Mississippi river, that was so 

 long regarded as completely isolating the two great coal-fields. 



The wide lithologic homogeneity and terranal continuity of 

 many of the beds constituting the coal measures permits single 

 units to be traced over surprisingly long distances. That the 

 Illinois and Missouri sections have never been matched up, as 

 it were, or that the Arkansas and Kansas-Missouri strata have 

 not been closely paralleled is doubtless due largely to the cir- 

 cumstances that public systematic investigations seldom trans- 

 gress state boundaries. The workers in one part of the province 

 are wholly without intimate knowledge of what has been done 

 elsewhere. The great force of this shortcoming led, not so very 

 long ago, to a critical personal inspection of the conditions ex- 

 isting in states contiguous to those in which principal investiga- 

 tions had been previously carried on. Among the facts discov- 

 ered were that the southern coal measures were mainly beneath 

 the base of the Missouri and Iowa measures, and that there was 

 actually great similarity between the general sections of the 

 Eastern Interior and "Western Interior Coal-fields. A host of 

 once incongimous features was thus readily explained. 



*Proc. Iowa Acad. Sci., Vol. XXIV, p. 53, 1917. 



