GEOLOGY: H. L. FAIRCHILD 
229 
the galactic plane, with nodes in longitude 70° and 250° (figs. 4a and 4b); 
(d) the diameter is of the order of 2500 light-years. 
The above results lead to a simple interpretation of star-streaming. The 
motion of an open cluster through the general star-fields of the equatorial seg- 
ment must give rise to stellar drifts, and it is a natural assumption that the 
observed streaming in the neighborhood of the sun is wholly due to such a 
cause. According to this view, stars of Stream I belong to the large moving 
cluster surrounding the sun; those of Stream II belong to the galactic field. 
The motion of the cluster as a whole is in the galactic plane, nearly radial from 
the galactic center, and there is considerable evidence of internal motion 
within the cluster. In all the details examined, this hypothesis appears to be 
in agreement with the observed systematic motions of the stars. 
1 Shapley, H., these Proceedings, 3, 1917, (479-484) ; Mt. Wilson Communication, No. 37. 
2 Slipher, V. M., Popular Astronomy, Northfield, Minn., 26, 1918, (8). 
3 Charlier, C. V. L., Meddelanden fran Lunds Astro omiska Observatorium, U psala, (Ser. 
2), No. 14, 1916, (1-108). 
GLACIAL DEPRESSION AND POST-GLACIAL UPLIFT OF 
NORTHEASTERN AMERICA 
By H. L. Fairchild 
Department of Geology, University of Rochester 
Communicated by J. M. Clarke, June 4, 1918 
The geophysical theory of isostacy is excellently illustrated by the up and 
down (diastrophic) movements of northeastern America in relation to glacia- 
tion. The amount and the area of land depression beneath the ice sheet, 
and the land uplift subsequent to the removal of the ice, is fairly proportionate 
to the thickness and extent of the latest ice cap. 
The fact is evident that the area covered by the latest continental ice 
sheet, the Labrador (Quebec) glacier, stood much beneath its present altitude, 
relative to sea-level, when the ice melted off ; and that the recent uplift has 
brought the land to its present position. The evidence of the uplift is abun- 
dant; many high-level beaches and sand-plains facing the open sea and extending 
far up the valleys in Canada, New England and New York, with the occurrence 
of abundant marine fossils hundreds of feet above the ocean. These facts have 
been recognized for quite a century, and many observations are recorded in 
the geologic literature of Canada and America. But up to the present time 
the full amount of submergence and the extent or limits of the drowned area 
have not been determined beyond dispute. The full amount of the down- 
and-up movement has nearly always been underestimated, because the con- 
spicuous or more evident marine features are generally of inferior and later 
