ABSTRACTS. 
87 
The introduction deals historically with the controversy of many years’ 
standing concerning G. pitcheri and the formations in which it occurs. 
An account of the fossil oysters of the Texas region and a classifica- 
tion of the Ostreidse follows. 
Contrary to the prevailing opinion that fossil oysters, on account of 
their great variation, are of little value in the recognition of strata, our 
authors are led by their observations to conclude “that certain forms of 
the Ostreidse possess very distinct characters, have definite geologic hori- 
zons, and are of the greatest value in stratigraphic work.” 
Sixty-one accepted species and varieties of fossil oysters are listed as 
occurring in Texas Cretaceous, and twenty-three indefinite or aban- 
doned species. Of the former, forty-seven are tabulated as occupying a 
definite range, “so that they become valuable landmarks in determining 
the exact geologic position of the beds in which they occur.” The fol- 
lowing topics are also discussed: “Historical Statement of the Discovery 
in the Texas Region of the Forms Referred to Gryphcea pitcheri , 'Morton.” 
“Differentiation;” “Geographic and Stratigraphic Distribution of the 
Lower Cretaceous Gryphseas;” “Specific Classification and Evolution of 
the Lower Cretaceous Gryphaeas;” and the bulletin closes with careful de- 
scriptions of six species, characteristic of the Lower Cretaceous, which 
the authors believe to merit recognition, supplemented by a brief state- 
ment of their relationships. 
The plates deserve especially commendation. Thirty are devoted to 
Gryphaeas; of the remainder, one is a view of a recent oyster bed, show- 
ing the profusion of molluscan growth, the other sections showing the 
stratigraphic occurrence of the Texas Cretaceous Ostreidae. 
II. 
Geology of the Edivards Plateau and Rio Grande Plain Adjacent to 
Austin and San Antonio, Texas, with Reference to the Occurrence of 
Underground Waters. By Robert T. Hill and T. Wayland Vaughan. 
Extract from the Eighteenth Annual Report of the United States Geo- 
logical Survey, 1896-97, part II, Papers Chiefly of a Theoretical Nature. 
Pp. 193-321. PI. xxi - lxiv. Washington, Government Printing Office, 
1898. 
This is, undoubtedly, one of the most important contributions to 
Texas Geology that has been made in recent yeans. While the underly- 
ing purpose of the authors has been to deal with the artesian water 
problem, they have really done much more. Not only has the strati- 
graphy of the region been carefully studied, but in many instances, as 
