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REVIEWS 



The generalization of the formational fauna by means of collections taken 

 at numerous and widely separated stations does much to eliminate the 

 false premise otherwise involved and doubtless the limit of error is still 

 farther reduced by considering not the faunas of individual formations but 

 of groups of formations. For this reason a grouping of the Kansas beds 

 was especially desirable. 



Some of the faunal modifications are regarded by the authors as the 

 result of conditions of sedimentation, while others are ascribed to barriers, 

 location and character not specified. Diversity of fauna at different points 

 in the same bed of limestone can clearly not be ascribed to the interference of 

 barriers nor probabH can the fact that the shales with which the limestones 

 alternate are usually almost barren of fossil shells, or at times contain 

 invertebrate faunas of appreciably different facies from the adjacent beds 

 of calcareous nature. Since now we have faunal variations, some of which 

 can clearly be assigned to environmental causes, the propriety seems 

 doubtful of explaining others by hypothetizing a different cause. 



The classification proposed by Messrs. Beede and Rogers may be sum- 

 marized as follows: The forty-six formations from the Cherokee shales 

 below, to, and including the Neosho formation, to which limits the authors 

 confine the Pennsylvanian, are divided into ten stages containing from one 

 to nine formations each, and the stages are again grouped into four series, 

 each of which contains two or three stages. The basis for this classifica- 

 tion is presented in the form of two charts, one of which is of such novel 

 construction that it requires the second as a key to it. 



This table seems especially designed to show the abundance of species 

 in the dift'erent formations, a fact to which the authors attach much import- 

 ance, because they connect it with the ability to migrate. They say, 

 "Another point of some significance which may be determined by the chart 

 is the time at which migration of individual species is most apt to occur. 

 It is well understood that the most vigorous species, represented by large 

 numbers of individuals, are the ones that migrate most readily, other things 

 being equal, and form the cosmopolitan elements of the various periods" 

 (p. 327). And also below on the same page: "Other things being equal, 

 it is believed that a species is more apt to withstand the vicissitudes of migra- 

 tion at this time [its culmination] than at any other on account of its greater 

 numbers and reproductive ability and greater vitality." Now some of 

 the fundamental facts in these statements seem doubtful to me. Are the 

 species represented by large numbers necessarily the most vigorous ? Are 

 the most vigorous species the ones that migrate most readily, other things 

 being equal ? And are other things ever equal ? As to the time of migra- 



