510 The American Naturalist [June, 
were doubtless many oscillations of the ice front, both during the gen- 
eral advance and the general retreat of the ice sheet. The extent and 
continuance of these oscillations is to be learned from study of the 
buried forests and vegetal deposits which lie between the eaplier and 
later sheets of till, and by such instances of erosion as may be clearly 
proved to be inter-glacial. But there does not seem to be evidence of 
any oscillations of the front sufficient to break the proper continuity 
_of the period.” 
The Colorado Formation and its Invertebrate Fauna.'— 
In a study of a collection of fossils from southern Colorado, Mr. T. 
W. Stanton found it necessary to review, not only the species definitely 
assigned to the Colorado Formation, but also a number of doubtful 
ones vaguely referred to the Cretaceous of Utah and New Mexico. 
The results of his investigations are published as Bull. No. 106 of the 
U. S. Geol. Surv., an octavo volume of 189 pages, and forty-five 
plates. In the compilation of the species, the nomenclature and 
descriptions have been carefully revised in all cases where better col- 
lections or additional facts seemed to make it necessary. Thirty-nine 
species are believed to be new to science. Mr. Stanton gives a com- 
parison of the lists of fossils to show that the invertebrate fauna of the 
Colorado formation cannot be subdivided into the well defined zones 
recognized in Europe, but the fauna on the whole may be regarded as 
the approximate taxonomic equivalent of the Turonian. i 
New Polyzoans from the Belgian Cretaceous.—Mr. Ed. 
Bergens is about to publish a descriptive work with plates of the Cret- 
aceous Polyzoans collected near Limbourg, Belgium. In this work 
the author figures a score of colonies from the Maestricht formation 
(Fox Hills) of great rarity. Among the known species is an examp e 
of Lichenopora diadema Gldfs. with an ovarian cell completely devel- 
oped ; an entire colony of Camerapora ; a colony of Retecava clathrata 
Gldfs. with the base rounded, figured in this rolled state as Neuropora 
cretacea by Von Hagenow. 
The other forms are new and many of them are referred to new 
genera. The author recognizes the genus Eschara, although it is com- 
posed of heterogenous elements, in order not to augment uselessly the 
synonomy, for a study of the soft anatomy has not yet allowed a defi- 
nite classification to be made. (Bull. Soc. Belge de Geol. Pal. et Hy- 
drog. T. VII, 1893). 
‘Bulletin United States Geological Survey, No. 106. The Colorado Formation 
and its Invertebrate Fauna. T. W. Stanton. Washington, 1893. 
