434 O. Meyer — Genealogy and Age of the Species, etc. 



Mr. Aldrich says, p. 303 : " Now if Dr. Meyer's theory is 

 correct we should find underneath the Claiborne beds the 

 Jackson and the Vicksburg formations." 



He then proceeds to show that several hundred feet of 

 marine Tertiary occur beneath the Claibornian, while no one 

 has demonstrated the existence of such strata below the Vicks- 

 burgian. Does now Mr. Aldrich expect that all those species 

 which lived during the Vicksburgian era at Vicksburg and 

 these alone lived also at every place in Alabama ? I explained 

 that the fauna of Wood's Bluff, a locality far below the Clai- 

 bornian, contains entirely new forms or /9 fossils, which two 

 classes do not indicate an age. It contains also a few Vicks- 

 burgian (one Jacksonian) d fossils.* This is as much as we 

 can expect according to my theory, and I gave this as my 

 "reason 6." Mr. Aldrich seems now to have the following 

 opinion about the range of, for instance, that variety of Pleuro- 

 toma lerebralis, which Conrad calls P. crislata : this variety 

 occurs in the lowest part of the whole Tertiary (Wood's Bluff 

 and lower); then follow 700 feet without it, then the whole 

 Claibornian and the whole Jacksonian without it and at the top 

 we find the same variety again in the Vicksburgian. While 

 according to my theory this form occurs probably only in the 

 Vicksburgian. Mr. Aldrich misunderstands my reasons 3 to 6 

 so thoroughly that it is perhaps useless to explain them at 

 length and to compare this explanation with what he says about 

 them. Three points only may be mentioned. 



There may be two different opinions about the relation of 

 the two varieties of a y fossil : 1. They have a common near 

 ancestor. 2. They are connected by direct descent. As all 

 agree that the Vicksburgian, Jacksonian and Claibornian was 

 deposited in different times, I think that the second opinion is 

 the best explanation. This — that this opinion is the most 

 probable — is the theory advanced in the first part of this essay. 

 Professor Smith calls this (p. 270): " inferences derived from 

 what he thinks should have been the course of evolution." He 

 as well as Mr. Aldrich think now that I base my reasons 3' 

 to 5 upon this theory. Only reason 5 is based upon it. Mr. 

 Aldrich says that the argument in reason 5 " passes his under- 

 standing." This is not my fault, it is not my duty to explain 

 to him the "biogenetische Grrundgesetz." Reasons 3 and 4 

 are general methods, independent of direct or indirect descent. 

 In reason 7 I cite the observation of an author and say what 

 conclusions I make from them. Mr. Aldrich need not accept 

 my conclusions if he thinks they are wrong, but he has no 



* Mr. Aldricli's mention of Natica Mississippiensis Conr. from Wood's Bluff (p 

 308 corroborates Professor Heilpriu's determination of this Vicksburgian fossil. 



