May 11, 1906.] 



SCIENCE. 



741 



boy Clays. There are, of course, well-defined 

 changes between the lower beds of the 

 Potomac, but such changes are gradual, due 

 to the diminution of old types, accompanied 

 by the increase and introduction of more 

 modern forms, while the flora as a whole 

 presents essential continuity. But in passing 

 to the Amboy Clays the case is wholly differ- 

 ent, and a wholesale change occurs whereby 

 few of the older types survive. At the same 

 time a great number of new plants appear, 

 and dicotyledons overwhelmingly predominate. 

 In view of this very striking change in the 

 character of the flora. Professor Fontaine puts 

 the very pertinent question, ' Why give the 

 name Potomac to this Group?' 



With respect to the much-debated question 

 of the precise relation which the Lower 

 Potomac bears to the Jurassic on the one hand, 

 and to the Cretaceous on the other, there can 

 be no doubt as to the transitional character 

 of the flora as presented by many of its com- 

 ponents, but the real ' question as to the 

 Jurassic or Lower Cretaceous age of the 

 Lower Potomac hinges upon the position of 

 the Wealden formation.' Previous studies of 

 the Lower Potomac plants by Professor Fon- 

 taine ° had led him to express the opinion 

 that they indicated a Lower Cretaceous age 

 agreeing with the Neocomian. This con- 

 clusion was based on the strong affinity of its 

 flora with that of the Wealden, it being as- 

 sumed that the view generally held as to the 

 position of the Wealden is correct, that is, 

 that it is the non-marine equivalent of the 

 Neocomian. In spite of the view held by 

 Professor Marsh, Professor Fontaine finds 

 that there has been no evidence suflicient to 

 cause a change of his former expression of 

 opinion, but, on the contrary, a good many 

 facts have come to light that confirm its cor- 

 rectness. 



These studies of the Potomac flora indicate 

 that the Potomac formation had a widespread 

 development on this continent, since it is not 

 only recognized in Virginia and Maryland, 

 but to the south and west it extends to 

 Tlaxiaco in Mexico; while on the north and 

 west it reappears in the Shasta of California, 



" U. S. Geol. Surv., Monograph XV., 1889, p. 348. 



the Lower Cretaceous of Queen Charlotte Is- 

 lands and in the Kootanie of Montana, British 

 Columbia and Alberta. 



D. P. Penhallow. 

 Montreal, 



April 27, 1906. 



A Respiration Calorimeter with Appliances 

 for the Direct Determination of Oxygen. 

 By W. O. Atwater and F. G. Benedict, of 

 Wesleyan University. Washington, D. C, 

 The Carnegie Institution of Washington. 

 1905. 4to, pp. 193, 49 figs. 

 The apparatus for investigations in human 

 nutrition described in this monograph has 

 been in process of development for about 

 twelve years and in its perfected form may be 

 safely characterized as the most elaborate in- 

 strument for physiological research at present 

 in existence. Descriptions of the apparatus 

 in its earlier form, and of the various improve- 

 ments and modifications introduced from time 

 to time, as well as accounts of investigations 

 carried on with it, have been published by 

 Professors Atwater, Woods, Rosa and Bene- 

 dict as bulletins of the Office of Experiment 

 Stations of the U. S. Department of Agricul- 

 ture and also as a memoir of the National 

 Academy of Sciences. 



The apparatus as described in the publica- 

 tions just mentioned consisted of a Petten- 

 kof er, or ' open circuit,' respiration apparatus, 

 the chamber of which was so constructed as to 

 serve likewise as a calorimeter. With this 

 instrument very accurate determinations were 

 possible of the income and outgo of carbon, 

 hydrogen, nitrogen, mineral matter and energy 

 in man, but the results were incomplete, in- 

 asmuch as no direct determination of the 

 amount of oxygen consumed by the subject 

 could be made. With the aid of a grant from 

 the Carnegie Institution, therefore, the au- 

 thors undertook a reconstruction of the appa- 

 ratus with this object in view. 



For this purpose they have reverted to the 

 earlier type of respiration apparatus, origi- 

 nated by Regnault & Eeiset and often desig- 

 nated as the ' closed circuit ' type, in which 

 the air after leaving the chamber of the appa- 

 ratus is freed from respiratory products, re- 



