July 28, 1905.] 



SCIENCE. 



107 



teleosts. D, batrachians and reptiles ; left- 

 hand line batrachians; right, dinosaurs; 

 middle, all other reptiles. E, birds, single 

 line. F, mammals ; left-hand line, non-pla- 

 cental; right, placental. G, land plants; 

 right-hand line dicotyledons and palms; 

 left, all other kinds. The dotted portion 

 of a part of those lines indicates some 

 doubt as to the epoch in which the kind 

 represented by such a line was introduced. 



DIAGRAM SHOWING TIME-RANGE OF CHIEF-KINDS OF 

 ANIMALS AND PLANTS. 



A, marine invertebrates; B, non- marine and 

 land invertebrates; G, fishes; D, batrachians and 

 reptiles; E, birds; F, mammals; G, land plants. 



This diagram thus represents the earliest 

 known epoch of existence of each of the 

 principal kinds of animals and plants, and 

 their continued existence through subse- 

 quent geological time. It is a significant 

 fact that, so far as can be judged by their 

 fossil remains, every kind represented on 

 the diagram began its existence with a 



comparatively high grade of its own types 

 of organization. The instances which will 

 be presented in support of the propositions 

 that were stated in the opening paragraph 

 of this article will necessarily be discon- 

 nected in their statement because, in an 

 article like this, there is only opportunity 

 to consider some of the more striking facts 

 selected from a multitude. 



The strata of lower Cambrian age con- 

 tain remains of the earliest forms of life 

 that are known to have existed upon the 

 earth.^ Large series of rocks, more or less 

 distinctly stratified like those of Cambrian 

 age are, in some regions, found underlying 

 the latter ; but no classifiable fossil remains 

 have been found in them, and little evi- 

 dence has been discovered that life existed 

 before the Cambrian age. The fossil re- 

 mains which are found in the Cambrian 

 strata pertain to all five of the invertebrate 

 subkingdoms, the vertebrata only being 

 absent; and remains belonging to each of 

 those five subkingdoms are found in all, 

 even the lowermost, of the Cambrian for- 

 mations. Representatives of those five sub- 

 kingdoms have continued to exist through 

 all the subsequent ages to the present time 

 in ever-varying forms within the limited 

 scope of their faunal rank, but those repre- 

 sentatives were evidently connected by con- 

 tinuous genetic lines, as is represented un- 

 der A on the diagram. So little change is 

 found to have occurred in the general or- 

 ganic rank of those subkingdoms that one 

 may justly assume nearly as high grade 

 for the earliest as for the latest members. 

 Those earliest known animal types either 

 originated with comparative suddenness 

 and then continued through subsequent 



^ For the present occasion I treat the reported 

 fossiliferous Algonkian rocks of Utah and Mon- 

 tana as not older than the lower Cambrian; but 

 even if they are really older, that fact Avill not 

 affect the validity of my argument, except to en- 

 force it. 



