i88 The Americcui Geologist. ^^^rch, i90i. 
establish is that the most recent general movements have been the same 
for the islands as for the coastline of southern California. I. H. o. 
A Remarkable Marl Lake. By Charles A. Davis. (Jour. Geol., 8, 
498-503) 
This paper supplements the preceding, describing the truly im- 
pressive deposit of marl in Littlefield lake, Isabella count}', Michigan, 
and showing that it is unquestionably due to the precipitating agency 
of Chara and Zonotrichia, chiefly through the exhalation of oxygen. 
\v. 0. c. 
CORRESPONDENCE. 
Notes on the KL\nsas-Oklahoma-Texas Gypsum Hills. — From 
the time of the earliest explorations of the great plains the gypsum 
hills have been objects of particular interest. Long and Marcy, 
among early explorers, and Hay, Cummins, Cragin, Prosser and 
Grimsley, among later geologists, have written extensively concern- 
ing these very interesting formations. Conspicuous on account of 
topography, color and position, these hills have ever excited an in- 
terest both popular and scientific. 
Geologically the gypsum hills are a part of the "red-beds" and 
are located near the center of that series. The red-beds consist of 
more than 2,000 feet of prevailingly red clays, shales and sandstones. 
The series extends from near the great bend of the Arkansas river 
in southern Kansas across Oklahoma and far into Texas before it 
finally disappears beneath the later Mesozoic and Cenozoic deposits. 
The age of the rock has long been a mooted question. In Texas it 
has been correlated with the Permian. In Kansas and Oklahoma it 
was for a number of years classified as Triassic, but the later geolo- 
gists have inclined to the opinoin that the red-beds of this region are 
of the same age as those of Texas, i. e., Permian. No fossils have 
been found in the Kansas beds and until the past year very few in 
Oklahoma. During the summer of 1900, however, the Oklahoma 
Geological Survey collected fossils from several localities in the red- 
beds. These fossils — vertebrates from the lower part of the series, and 
invertebrates from the upper part — indicate that in Oklahoma at least 
the red-beds belong to both the Permian and Triassic. 
Throughout the entire thickness of the red-beds the rock is 
strongly impregnated with mineral salts. In the lower part common 
salt predominates. In Oklahoma there are no fewer than four large 
salt planes, and numerous smaller ones. In general the salt planes 
are confined to a definite horizon. Even among the saliferous hori- 
zons gypsum is of frequent occurrence. Seams of selenite and satin 
spar are often abundant. 
