Geology and Mineralogy. 177 



and Arundel, doubtfully referred by Bibbins to Upper Jurassic 

 and ascribed to the Lower Cretaceous by Professors Ward and 

 Fontaine. Neither of the latter now hesitate to regard the flora 

 of the Potomac as essentially Wealden and Lower Cretaceous, 

 on the basis that the Wealden is the non-marine equivalent of 

 the Neocomian, this being of course the most interesting geo- 

 logic question dealt with by the volume. As Marsh held the 

 Potomac to be Jurassic on the basis of its pre-Neocomian equiva- 

 lency, there is of course no hiatus in the observations of those 

 who have dealt with the upper boundaries of the Jurassic — 

 always so uncertain because in both Europe and America the 

 marine Jura is followed by the formation of fresh- to brackish- 

 water beds most difficult to divide, though containing the most 

 striking fossils. The reviewer had the pleasure of hearing 

 Professor Marsh defend his hypothesis many times, and perhaps 

 mainly because of that fact finds some difficulty in regarding the 

 question as fully and finally closed. It does appear, however, 

 that, as Professors Ward and Fontaine insist, the evidence that 

 the Wealden is an unconformable transition series has much 

 increased. It is also to be urged that the direct evidence of 

 marine Jurassic superposition, as in the still doubtful cases like 

 the Glen Rose beds of the Trinity group in Texas, must still be 

 awaited with much interest ; that the origins of animal and 

 plant forms are always being traced further and further back ; 

 and finally, that it is a very significant fact that the dicotyls 

 creep in as if by stealth in both the Arundel (Hogersia), and 

 near the Minnewaste limestone in the Black Hills (Sapindopsis). 



This appearance of new species with a strong invasive power 

 may well mark profound physical changes within Potomac time, 

 though such may be locally difficult to determine. G. r. w. 



2. Geology and Paleontology of the Judith River Beds / by 

 T. W. Stantok and J. B. Hatcher. Bull. 257, U. S. Geol. Surv., 

 1905, pp. 174, pis. 19. — During the year 1902, there was pub- 

 lished a series of short, but interesting discussions between 

 Osborn, Hatcher and Stanton, showing considerable difference of 

 opinion regarding the position of the Judith River beds and 

 their correlation with the Belly River beds of Canada. These 

 difficulties were worked out satisfactorily in the field during 1903, 

 in northern and central Montana and adjacent areas of Canada. 

 The principal conclusions of Stanton and Hatcher are as follows : 



" (1) The Judith River beds are distinctly older than the 

 Laramie, being separated from the latter by at least several hun- 

 dred feet of marine shales identical in their faunal and lithologic 

 features with the Pierre to which we have given the local name 

 Bearpaw shales, from the Bearpaw Mountains about which they ' 

 are well exposed. 



" (2) The Belly River beds of Canada are identical with the 

 Judith River beds of Montana. The name Judith River beds, 

 having priority, should be the accepted name for this formation 

 and the terms Belly River and Fish Creek should be dropped. 



