390 The Amencan Geoioyts: June, 1896 
REVIEW OE RECENT GEOLOGICAL 
LITERATURE. 
The Saint Peter Sandstone. By F. W. Sardeson. (Bulletin of the 
Minnesota Academy of Natural Sciences, vol. iv, ao. 1, pp. 64-88, plates 
_ I. 189(5.) In this paper Dr. Sardeson discusses briefly (rather too 
briefly we believe) the thickness, geographical and geological distribu- 
tion, structure, lithologic and paleontol<>e-ic characters, physical rela- 
tions, stratigraphic position, correlation and origin of the Saint Peter 
sandstone, While not much new light is thrown upon the vexed 
problems connected with this remarkable formation, the paper is never- 
t heless of value because it affords a convenient arrangement of the more 
important facts concerning the subject that have accumulated during 
the past fifty years. In discussing the origin of the Saint Peter Dr. 
Sardeson suggests a theory to explain the purity of the sandstone that 
seems to be as plausible at least as the chemical theory. " The purity 
of the Saint Peter sandstone, the paucity of its fossils and its variable 
depth are all due to the effect of percolating waters and were not origi- 
nal characters, and, further, that the supposed unconformability at its 
base may have been produced solely in this manner. That is. that the 
Saint Peter has simply had all soluble material washed out of it, that it 
is thus reduced in thickness, and that the now dolomitic formations 
immediately beneath have been attacked in a similar manner and 
reduced, the whole process causing a shifting of the sand sufficient to 
produce inequalites in its thickness." 
In our opinion the greatest value of the paper lies in its paleontologi- 
cal part. Heretofore the known fauna of the Saint Peter was extremely 
limited, but, mainly through the efforts of Dr. Sardeson, we know of 
at least twenty-eight species, of which nineteen are described as new, 
one was described some years ago by Prof. N. H. Winchell, five are 
referred more or less doubtfully to well-known Trenton species, and 
three are too ill preserved to be determined satisfactorily. Excepting 
five species (three Brachiopoda and one each of Bryozoa and Spongia) 
the fauna is entirely molluscan (Lamellibranchiata thirteen, Gastropoda 
seven. Cephalopoda three) and in this respect compares very well with 
the fauna of the underlying Shakopee dolomite. But the individual 
species are widely different, while they agree much better with Trenton 
types. 
Considering the general imperfection of Saint Peter fossils, a critical 
review of Dr. Sardeson's classification of his new species may not be 
quite fair. Still, it seems to us, he might in several instances have 
reached without much trouble more satisfactory results. Thus his 
Modiolopsis affinis, M. gregalis and M. senecta cannot possibly belong 
to Modiolopsis, while his M. litoralis should have been referred to 
Orthodesma. What led him to place his species absimilis under 
Tellinomya we cannot imagine. In the shape of the shell and style of 
its surface marking it is totally different from all of the numerous 
