440 C. A. White — Loiver Cretaceous of the Southwest. 



Principal Conclusion. 



Of the numerous conclusions to be drawn from this research, 

 we here only direct the reader's attention to what we consider 

 the most important one, namely : That the mean temperature 

 of the sunlit lunar soil is much lower than has been supposed, 

 and is most probably not greatly above Zero Centigrade. 



Post Scriptum. 



I would ask to be allowed here to state that the very con- 

 siderable expense for the special means and reduction of the 

 preceding series of lunar researches was borne by one of the 

 most generous and disinterested friends that Science has had in 

 this country, the late William Thaw, of Pittsburgh. By his 

 own wish, no mention of his name was made in previous pub- 

 lications in connection with the results so greatly indebted to 

 his aid. His recent death seems to remove the restriction im- 

 posed by such a rare disinterestedness. 



Art. LIY. — The Lower Cretaceous of the Southwest and its 

 relation to the underlying and overlying formations y by 

 Charles A. White. 



[Published by permission of the Director of the U. S. Geological Survey.] 



The Cretaceous strata which constitute what has become 

 known as the Texas section are referable to two natural divisions 

 which, in North American geology, may be properly designated 

 as Upper and Lower Cretaceous respectively, although not im- 

 plying thereby that they are respective^ the equivalents of the 

 Upper and Lower Cretaceous of Europe.* The fossil contents 

 of each division indicates that each represents an unbroken 

 portion of Cretaceous time ; and the paleontological contrast 

 between the two divisions indicates that there is a time hiatus 

 between them. 



The Upper Missouri river section of Meek & Hayden, from, 

 and including, the Dakota Group upward, may be taken as 

 representing the upper division, while the lower division, which 

 I have heretofore designated as the Comanche series, has been 

 often omitted by geologists from their sections of the North 

 American Cretaceous, or its relation to other formations has 

 been imperfectly understood, or stated. Strata of the lower 

 division have not been discovered to the eastward of the 95th 

 meridian, and, with the probable exception of a locality in 



*Id my future writings upon the North American Cretaceous I propose to 

 make its division into Upper and Lower Cretaceous still more general. 



