IOWA ACADEMY OF SCIENCES. 57 



study of life is confined to a single locality. Of course to try to make the rule 

 general would be to deny the theo'y of evolution. Since life is largely dependent 

 upon climatic conditions, it follows that a sudden change in these conditions means 

 a sudden change of life. So that, if in passing from one stratum to another, we 

 find a considerable change in fossil forms, we must accept it as evidence of change 

 of conditions under which the depositions took place. 



Now, as I have already stated, we find such comparatively marked changes of 

 fossil forms at several places in the Burlington limestones. Knowing such to be 

 the case I have been on the lookout for further evidences of changes in the way of 

 erosion, unconforinability, etc. 



It has generally been accepted that the deposition of the whole lower Carboni- 

 ferous group in southeastern Iowa was uninterrupted. I quote from White, Greol. 

 of Iowa, 1870. Vol. 1, page 202. "The accumulation of the strata which compose 

 all the formations of the sub-Carboniferous group in southeastern Iowa, from the 

 lower Burlington limestone to the Saint Louis limestone, inclusive, was evidently 

 uninterrupted." And this seems to have been the generally accepted idea. 

 White admits the change of fossil forms, but limits the changes to siliceous beds 

 only, and advances the theory that life died out owing to the waters becoming 

 charged with siliceous material. He makes no statement of the tact that some of 

 the most distinct lines of change are at intervals between the lower and upper 

 flint beds, and also below the lower one. It is most likely, too, that the flint beds 

 mark gradunl rather than sudden eras of. change. However, of this I will say 

 more later. 



White gives 50 feet as the thickness of each division of the Burlington lime- 

 stone, making 100 feet for the two. Now, at Burlington, the typical locality, the 

 two together measure scarcely more than 50 feet. Of course there are deposits at 

 other places in southeastern Iowa belonging to the Burlington series which are not 

 represented at Burlington iti:elf. And no doubt the complete section of the two 

 divisions together would reach 100 feet. Now, while there was a cessation of 

 deposit and corresponding absence of life in one locality, the rock building was 

 steadily going on at other points not far distant. So that while 50 feet may be the 

 maxirrum thickness at any one locality, the total thickness of the complete series 

 mieht easily be 100 feet. 



The lower division of the Burlington limestones gives a more continuous sec- 

 tion than the upper. As to fossil forms there are some pretty distinct lines of 

 change, but so far I have been unable to find any evidence of a corresponding era of 

 disturbance. There is no positive evidence that there was a cessation of deposition 

 The surfaces of some of the strata have a water-worn appearance, but no erosion 

 has so tar been discovered. It would not surprise me, however, to hear of such 

 evidence having been found. The lower half of the lower division is well-bedded 

 and seems to have been laid down in comparative quiet waters. The upper half 

 is poorly bedded and contains many flint bands and irregular pockets of coarse 

 sandy clay. It shows much disintegration. 



As to the origin of these flint bands there has been a great deal of speculation, 

 but so far no very satisfactory theory has been advanced. An examination of the 

 beds will show that life did notsuddenly cease with the advent of siliceous material. 

 Frequently layers are found which are literally covered with fossils. My attention 

 was first called to this fact by Mr. Chas. R. Keyes about two years ago while 

 examining the Burlington limestone at Louisiana, Mo. I have since found it to be 

 true at Burlington and other places. The fossils are ahvavs fully solicified, 



