60 '/'//< American Geologist. July. 1893 
imentary strata from Pigeon river and the northeastern border of 
Minnesota to Port Arthur and Thunder, Black and Nipigon bays. Pre- 
vious observers have considered these extensive trap sheets as overflows; 
but from many observations Dr. Lawson maintains that none of them 
associated with the Animikie formation are of that character, but that 
they are all intrusive in their origin and are of the nature of laccolitic 
sills. Some of these sheets reach beyond the Animikie and cap mesa- 
like hills and cliffs of the later Nipigon or Keweenawan scries. There, 
likewise, they were evidently intrusive sheets, so that their date was 
later than both the Animikie and Nipigon periods. The author names 
these intrusive trap beds the Logan sills in honor of Sir William E. 
Logan. 
The Norian of the Northwest. By N. H. Winchell,. The preface of 
the bulletin containing Dr. Lawson's papers consists of 32 pages by 
Prof. Winchell, reviewing the history of investigations of the gabbro 
north of lake Superior and comparing it with the gabbros at the base 
of the Keweenawan in the typical region of Keweenaw point and in 
parts of northern Wisconsin. Their correlation with the similar anor- 
thosyte formations in eastern Canada, where they were studied by 
Logan and Hunt and named by the latter geologist Norian from their 
fine development at Esmark, Norway, and in New Hampshire where 
Prof. C. H. Hitchcock recognizes them in the district of the White 
mountains, is regarded as so highly probable that the application of the 
name Norian is advocated for their occurrence in the Northwest. Pro- 
fessor Winchell further discusses the relationship of the gabbro and 
anorthosyte rocks of northeastern Minnesota with certain red meta- 
morphic sedimentary rocks of the Animikie series, which in extensive 
belts appear to have been the result of fusion by the igneous agencies 
producing the gabbro. This view would place the age of the gabbro 
later than the time suggested by Lawson, so that perhaps, in the opin- 
ion of Prof. Winchell, the gabbro may have been the deep molten mag- 
ma from which the the diabase outflows in the Keweenawan series were 
derived, as suggested by Irving. If this be true, the unconformity of 
the latter in some places upon the former and derivation of boulders 
from it imply that the Keweenawan period comprised stages of land 
oscillation and considerable subaerial erosion. But Prof. Winchell 
notes the occasional occurrence of detached masses of the anorthosyte 
rocks having as large dimension as 200 feet enclosed within a matrix of 
the Keweenawan diabase; and he inclines to the belief that usually or 
perhaps always where the anorthosytes occur in place they are separat- 
ed from the Keweenawan by intervening Animikie beds, which often 
are much metamorphosed. 
Republication of Conrad's Fossil Shells of the Tertiary Forma- 
tions of North America. By Gilbert Dennison Harris. Washing- 
ton, 1893. 121 pp., 20 pis. 
It is a curious fact that a work so indispensable to students of 
American Tertiary paleontology as Conrad's "Tertiary Fossils" should 
be so rare that few even among specialists in that field are fully aware 
