No. 413. REVIEWS OF RECENT LITERATURE. 2 
423 
the Eocene Green River shales of Wyoming. Most of the fossil gar 
pikes of America have been hitherto known from bare fragments 
scantily described. Mr. Eastman’s specimen of Z. atrox is especially 
complete, as large as an alligator gar, and very much like it in 
appearance. In fact it “lacks any positively archaic features,” and 
Mr. Eastman regards it as “obviously the direct progenitor of the 
alligator gar, Z. Zristechus.” Mr. Eastman finds no trace of the 
earlier ancestry of Lepidosteus. The gar pikes “ blossom forth sud- 
denly and fully differentiated at the dawn of the Tertiary without 
the least clue to their ancestry, unheralded and unaccompanied 
by any intermediate forms, and they have remained essentially 
unchanged ever since.” 
In the Bulletin of the Kansas University, Vol. I, No. 2, Prof. S. 
W. Williston describes and figures many teeth of sharks found in 
the Cretaceous rocks of Kansas, his paper being a very useful con- 
tribution to this difficult branch of paleontology. In the matter of 
nomenclature, apparently, Agassiz’s name, Oxyrhina, should not be 
used instead of the earlier Isurus of Rafinesque, and Scylliorhinus 
of Blainville has unfortunately clear priority over Scyllium Cuvier. 
PETROGRAPHY. 
Geology of the Black Hills. — Irving’s contribution to the geology 
of the Northern Black Hills adds a great deal to our knowledge of 
this interesting region, especially from the point of view of petrog- 
raphy. The author agrees with Crosby, rather than with Russell, 
in regarding the larger intrusives of the district as laccolites and not 
as plugs. He finds also an abundance of sills and dikes. The 
dikes characterize the Algonkian slates, the sheets and laccolites 
the Cambrian shales. The Carboniferous limestone is almost devoid 
of intrusions of any kind. The principal types of rocks recognized 
are a quartz-egirite-porphyry, tinguaite, phonolite, trachytoid-pho- 
nolite, quartz-porphyry, mica-diorite-porphyry, dacite, tonalite, and 
augite-vogesite. The phonolites and quartz-porphyries are the 
most abundant types, with the quartz-egirite-porphyries and the 
diorite-porphyries fairly abundant. There is such an intimate 
gtadation between the different types that they appear to be related 
genetically. In the pre-Cambrian rocks, dikes and possibly plutonic 
