jSeptesibee 9, 1898.] 



SCIENCE. 



317 



much their present courses, meandering 

 through alluvial flats " (p. 481). An eleva- 

 iiory movement began in the succeeding or 

 ■Colorado epoch, and this was succeeded by 

 .an uplift on the Atlantic and Gulf coasts, 

 and the continued upheaval in the interior 

 resulted in the deposition of the Laramie 

 brackish and fresh- water beds. There were 

 rsimilar widespread subsidences and up- 

 heavals in South America, the Andean 



■ chain being in large part upheaved at the 

 close of the Cretaceous. 



In the Cretaceous period there were such 

 differences in the distribution of the fossils 

 as to lead Eomer, from his explorations in 

 Texas as early as 1852, to consider that the 

 resemblance of the fossils of Texas, Ala- 

 bama and Mexico, with the "West Indies 

 and Colombia, to those of southern Europe 

 were due to differences of climate, a view 

 reiterated by Kayser (p. 283). Scott also 



■ states that the Lower Cretaceous beds of 

 Texas show faunal resemblances which ally 

 them to the Portugal and Mediterranean 

 beds, while the faunal relations of South 

 American Lower Cretaceous strata are 

 closely like those of northern and western 

 Africa. 



The biological changes at the beginning 

 of the Upper Cretaceous were correspond- 

 ingly notable. Vast forests of conifers, 

 palms, and especially of deciduous trees, 

 such as the oak, sassafras, poplar, willow, 

 maple, elm, beech, chestnut and many 

 others, clothed the uplands, while in the 

 jungles, on the plains and in the openings 

 of the forests gay flowers bloomed. The 

 flora must even then have been, compara- 

 tively speaking, one of long existence, be- 

 cause highly differentiated composite plants, 

 like the sun-flower, occur in the Upper Cre- 

 taceous, or Raritan clays, of the New Jersey 

 coast. It may be imagined that, with this 

 great advance in the vegetation, the higher 

 flower-visiting insects must have correspond- 

 ingly multiplied in number and variety. 



While the changes of level did not afiect 

 the abysses of the sea, the topography of the 

 shallows and coast was materially modi- 

 fied, and to this was perhaps largely due 

 the extinction of the ammonites and their 

 allies.* It is not impossible that the un- 

 coiling of the ammonites into forms like 

 Scaphites, Crioceras, Helioceras, Turrilites 

 and Baculites were originally perhaps dis- 

 tortions due to physical causes somewhat 

 similar to those which produced a loosening 

 or uncoiling of the spire in Planorbis. 

 These variations or distortions of the pond 

 snail, signs of weakness, the result either of 

 pathological conditions or of senility, were 

 due to unfavorable changes in the environ- 

 ment, such as either a freshening of the 



*After preparing this address I find that Wood 

 thirty-six years ago more fully discussed this matter 

 and mentioned the same cause I have suggested. 

 "This disappearance," he says, "of the Ammon- 

 itidaj and preservation of the Nautilidse we may infer 

 was due to the entire change which took place in the 

 condition of the shores at the close of the Cretaceous 

 period ; and this change was so complete that such of 

 the shore followers as were unable to adapt them- 

 selves to it succumbed, while the others that adapted 

 themselves to the change altered their specific char- 

 acters altogether. The Nautilidje having come into 

 existence long prior to the introduction of the 

 Ammonitidse, and having also survived the destruc- 

 tion of the latter family, must have possessed in a 

 remarkable degree a power of adapting themselves to 

 altered conditions." On the other hand, the di- 

 branchiate cephalopods (cuttles or squids), living in 

 deeper water, being ' ocean rangers,' were quite inde- 

 pendent of such geographical changes. Wood then 

 goes on to say that the disappearance of the tetra- 

 branchiate group affords a clew to that of the Mesozoio 

 saurians, and also of cestraciont sharks, whose food 

 probably consisted mainly of the tetrabranchiate 

 cephalopods. " Now the disappearance of the Tetra- 

 branchiata, of the cestraoionts and of the marine 

 saurians was contemporaneous ; and we can hardly 

 refuse to admit that such a triple destruction must 

 have arisen either from some common cause or from 

 these forms being successively dependent for existence 

 upon each other. ' ' He also suggests that the develop- 

 ment of the cuttles ' has been commensurate with 

 that of the cetacean order, of some of which they 

 form the food.' {Phil. Mag., XXIIL, 1862, p. 384.) 



