WAKD.] DISCUSSION OF THE TABLE. 515 



DISCUSSION OF THE TABLE OF DISTRIBUTION-. 



In attempting to compare and discuss a few of the more salient points 

 which this table brings to light, it will perhaps be most convenient to 

 consider the several groups of the systematic arrangement in their de- 

 scending order from the primary subdivision into the two great series 

 down to the ultimate subdivision into species. Preliminary to this a 

 few of the leading facts need to be set down. 



The whole number of species enumerated in the table is l,5i0, of 

 which 286 are Cryptogams and 1,254 are Phanerogams. The Crypto- 

 gams consist of 119 cellular and 167 vascular, and the Phanerogams of 

 115 Gymnosperms and 1,139 Angiosperms. The Angiosperms embrace 

 160 Monocotyledons and 979 Dicotyledons, and this last subclass is 

 made up of 467 apetalous, 406 polypetalous, and 106 gamopetalous 

 plants. These are the primary groups into which the vegetable kingdom 

 is divided in the natural system, and, with the occasional exception of the 

 last two, vegetable paleontologistsalinostunanimouslyadopttheorderin 

 which they have Just been stated, which is also that of the table. They 

 do this chiefly because it best represents the order in which these groups 

 have appeared in the geological history of the earth, and their relative 

 abundance in the several ascending strata. This, however, is true only 

 as a general proposition, and may not hold in special cases, particularly 

 when adjacent formations are compared. It cannot, therefore, be ex- 

 pected to prove literally true of the three formations we are here consid- 

 ering, nor to have any very great weight in determining the age of the 

 Laramie group. Doubtless if we knew the entire flora of that group, and 

 also the floras of the upper Cretaceous and the Eocene, such a compari- 

 son would have considerable weight and serve in large measure to fix 

 the time at which the first of these floras flourished relative to that of 

 the other two. But while we need not anticipate great results in this 

 direction with things as they are, our table enables us to make this com- 

 parison, and it will be interestiug, to say the least, to do so. 



In comparing the leading floral elements of these three formations, 

 however, it is evident that we cannot use the net figures as given above, 

 on account of the occurrence of a considerable number of species in 

 more than one of them, sometimes in all three. The number of such 

 coincidences amounts in our table to twenty-four, making the gross en- 

 tries in the three columns 1,564 instead of 1,540, and the former of these 

 numbers must be taken as a basis of comparison. These slight additions 

 will be scattered through the different groups, affecting them all more or 

 less. The changes will not, however, at all vitiate the conclusions to be 

 drawn. It is clear that the element to which we must attend is the 

 proportion which the several vegetable groups bear to the total num- 

 ber from each formation, and that a comparison of these percentages in 

 the same group for the three formations will afford us all the basis there, 

 is from which to draw conclusions. 



