June 30, 1 881] 



NATURE 



191 



Buoyancy of Bodies in Water 



In Nature, vol. xxiv. p. 166, Dr. W. Curran says:— "It 

 is, I think, generally assumed in books and courts of law that all 

 bodies, human and bestial, sink as a rule in w ater as soon as life 

 is extinct." How far this statement may be true as regards 

 animals generally, I am not prepared to say, but it certainly does 

 not hold good as regards the reindeer. The Eskimos spear 

 many reindeer whilst crossing lake=, and it sometimes occupies 

 them an hour or two in "towing" them all to land, yet it is a 

 rare exception that any are lost by sinking, even of the full-gr.wn 

 males, which in autumn are heavily weighted with large antler--. 



4, Addison Gardens, June 25 John Rae 



An Optical Illusion 



Will you allow me to add something to the letter from 

 William Wilson in Nature, vol. xxiv. p. 53. 



I. The results described may be produced without bending 

 the card or using a square hole. A flat card, with a pin-hole, is 

 held some distance from the eye, and a pin moved so as to be in 

 a right line between the eye and the hole ; the results described 

 by Mr. Wilson follow. 2. Some few trials may be necessary in 

 order to get a clear image (if this is the prober term), but it will 

 be found that considerable variation in the distances from the 

 eye to the pin and from the pin to the hole can occur w ithout 

 destroying the effect. 3. The image seems to n.e to be close to 

 the card in every case, while the distance frcm the eye to the 

 card may vary a great deal. Clarence M. Boutelle 



State Norn.al -School, Winona, Minn., U.S , June 10 



Resonance of the Mouth-Cavity 

 In reply to Mr. George J. Romanes, I beg to say that the 

 object of my communication printed in Nature, vol. xxiv. p. 100, 

 was to show that the mouth-cavity will give a distinct resonance 

 to different rates of vibration already in tlie air by being shaped 

 suitably for each of them (and providing they come within its 

 limit). The mouth thus gives the means of analysing the com- 

 posite nature of sound. Any one successfully relocating my 

 experiments given on pp. 100, 126, would be satisfied that they 

 pointed to something different to the boys' amusement mentioned 

 in Mr. Romanes' letter (p. 166). 



5, West Park Terrace, Scarborough John Naylor 



American Cretaceous Flora 



In several of the interesting and valuable papers on the Ter- 

 tiary flora which Mr. J. Starkie Gardner has contributed to the 

 English journals he has referred to the fossil plants in our Cre- 

 taceous rocks as representing a flora really Tertiary in character ; 

 and, influenced by the modern aspect of the plants contained in 

 our Dakota group (Lower Cretaceous), he has expressed a doubt 

 whether even that should be regarded as truly of Cretaceous age. 

 In a former numb;r of NATURE I endeavoured lo show that our 

 Dakota flora was Cretaceous, inasmuch as it is found in rocks 

 which are overlain by several thousand feet of strata contain- 

 ing 'many moUusks, fishes, and reptiles which are everywhere 

 recognised as Cretaceous, and none that are Tertiary. 



Mr. Gardner w as not however convinced by my facts or argu- 

 ments, and in the April number of the Popular Science Rtz'iew 

 he reiterates and emphasifes his formerly expressed opinion, 

 referring all our Cretaceous strata to the Maestricht beds, and 

 intimating that, in common w ith that formation, they should be 

 separated from the Cretaceous system. His language is as 

 follows : — 



" The presence of Mosasaurus in the Maestricht beds, and the 

 far newer aspect of its fauna, show that it must have belonged 

 to an altogether different period, probably the one represented 

 in America by a great so-called Cretaceous series containing a 

 mixture of Cretaceous and Tertiary moUusks, dicotyledonous 

 plants, and Mosasaurus 



" No American or European so-called Cretaceous land flora 

 can be proved to be as old as our White Chalk." 



Now in no spirit of criticism, for I appreciate and value the 

 excellent work that Mr. Gardner is doing, but simply for the 

 vindication of the truth of geology, I ask him to qualify these 

 statements. 



I am impelled to this course by the following facts : — 



In our Triassic series we have in some places beds of coal and 



the remains of a vegetation decidedly Mesozoic in character, 

 consi-ting of Cycads, Conifers, and Ferns, l.ut, as far as we yet 

 know, withi ut a single Angiospcrm. 



In the Jurassic age the eastern half of the North American 

 Conti iient formed a land-surface, for the seo iments of the Jurassic 

 sea are confined lo a somewhat irregular area in and west of the 

 Rocky Mountain belt. 



Of the Jurassic flora of North America we as yet know little 

 or nothing ; but the continent that bordered the Jurassic sea 

 ultimately became covered with a nei>-, varied, and highly- 

 organised flora, of which the origin is y<,t unknown. 



In the Cretaceous age all the continent lying east of the 

 Wasatch Mountains was affected by a subsidence which brought 

 the sea in f rf m the Gulf of Mexico with a front 1000 miles 

 wide, and the great inland sea thus formed gradually extended 

 northward till it renched nearly, if not quite, to the present 

 shore of the Arctic Ocean. 



The waves of the Cretaceous sea in their advance swept before 

 them a shore tliat was covered with a luxuriant forest of at least 

 one hundred species of Angi^ spermous trees ; and the remains of 

 trunks and twigs, leaves and fruit, were buried up in the sheet 

 of beach material which accumulated all along the advancing 

 shore line, and which now forms the Sandstones of the Dakota 

 group. Up to the present time very few mollusl-s have been 

 found in this group, and they are not sufficient to fix with exact- 

 ness its relation to the Cretaceous series of other countries. 1 he 

 plants, too, are distinct from any found in Europe, though they 

 inclu<ie, with many extinct forms, genera which are common in 

 the living forests of America, such as Qiierciis salix, Magnolia, 

 Ftt.;us, LiijuUambar, Liriodcndroii, &c. 



When the subsidence which produced the Dakota group was 

 at its maximum the sea stood several thousand feet deep over the 

 central portion of the trough between the Allcghanies and the 

 Wasatch Mountains, and here we now find at least two thousand 

 feet of marine, calcareous, organic sediment, which have 

 furnished hundreds of species characteristic of the Cretaceous 

 age, and a large number that are identical with those contained 

 in the Upper Greensand and Chalk of Europe. 



It is true that up to the pre; ent time no Neocomian fo-sils 

 have been found in the interior of the Contiiient, hut -with that 

 exception the entire Cretaceous series of the Old World Ls repie- 

 sented there. Hence it is not true that our Cretaceous " cc'n- 

 tains nothing so old as the Chalk." 



Nor is it true, as intimated by Mr. Gardner, that our "so- 

 called Cretaceous rocks" contam a Tertiary flora and fauna, as no 

 Tertiary species of either has yet been found there. The flora 

 of the Dakota group is more modern in its aspect than that of 

 the Low er and Middle Cretaceous of Europe, liut its plants are 

 specifically different from any found in Europe in our Middle 

 Cretaceous (Colorado groujj). Upper Cretaceous (Laramie group), 

 or Tertiary beds (of Green Kiver, Fort Union, and Oregon). 

 The facts apparently indicate that the earliest development of 

 Angiospermous plant-life took place here, and this in a tcmpei-ate 

 flora of which the descendants long afterwards — in Tertiary 

 times — occupied Greenland, Spitzbergen, &c., and spread by 

 land connections into Europe and Asia. 



The best authorities we have had on questions relating to the 

 Cretaceous faui a— Messrs Gabb and Meek — were fully agreed 

 in regarding our Middle Cretaceous as of the a^e of the Chalk. 

 Mr. Gabb divided the Cretaceous series ol California into four 

 members — 



1. The Tejou group. 



2. The Martinez group. 



3. The Chico group. 



4. The Shasta group. 



Of these the oldest, or Shasta, group was regarded 1 y him as 

 of Neocomian age, the Chico and Martinez groups — which 

 should perhaps be united — as the representatives of the Upper 

 and Lower Chalk, aud the Tejou gi"oup as the equivalent of the 

 Maestricht beds. 



The coal-beds and the fossil plants of Vancouver's Island lie 

 at the base of the Cretaceous series as it exi-ts there, and the 

 molluscous remains indicate that it is the equivalent of the 

 Chico group. The plants are apparently all distinct from 

 those of the Dakota group of the interior. They include 

 palms rnd cinnamon':, and evidently grew in a warmer climate 

 than that \ hich produced the temperate flora of the Lower 

 Cretaceous of Kansas, Nebraska, and the Atlantic coast. 



Among the Vancouver Island Cretaceous plants is one well- 

 known species, Sequoia Reichenbachii, H., which is found in 



