Correspondence. 195 
ley was continued out into the gulf of Mexico and two buried channels 
ran east and west from cape Sable, the former being called the Baha- 
man and the latte;- the Floridan. Over the col between the two flows 
the gulf stream. 
In a second paper Dr. Spencer described the geology of Mexico and 
from recently published maps of rhat country took occasion to point out 
that the coast plateau is a continuation of that of Texas and rose to the 
hight of 1700 feet. It is of Lafayette and Columbian date. The cen- 
tral cretacean plateau rises to 800(' feet and forms the largest area. The 
isthmus of Tahuantepec now reaches a hight of only 800 feet and was 
in late Pliocene and early Pleistocene times completely submerged al- 
lowing passage between the two oceans. The last conclusion is war- 
ranted by the resemblance between the shallow water faunas of the two 
sides of the isthmus while the inhabitants of greater depth show little 
resemblance. The Pliocene strata have in some places been elevated to 
a hight of 8000 feet. 
Prof. P. B. Taylor took up the controverted subject of Niagara and 
advocated the view that the wide portion of the gorge below the whirl- 
pool and a small part of that above it was cut by the river imme- 
diately after the retreat of the ice and when the whole water of the lakes 
was poured over the c;ataract — that the narrow part above is the work 
of the smaller stream when part of the water was drawn off by the Ni- 
pissing outlet into the Ottawa river, and that the wider portions from 
the cantalever bridge to the present falls is due to the greater body of 
water ensuing on the uplift and closing of that outlet. Some discussion 
followed partly in favor of Mr. Taylor's views and partly in opposition. 
In a second paper Mr. Taylor pointed out a possible, now extinct, chan- 
nel from the Georgian bay to the river Trent by way of lake Simcoe, al- 
so dependent for its existence on the closing of the Nipissing channel. 
The last paper read was by Mr. W. H. Scherzer of Ypsilanti, Mich., 
and gave a clear and interesting account of the strata in the vicinity of 
Detroit. It concerned chiefly Monroe and Wayne counties. Large 
quarries of the Corniferous limestone expose about 15 acres of the rock, 
which has been quarried to a depth of 30 feet, the whole thickness be- 
ing 100-150 feet. It contains much chert. The Onondaga and Water- 
lime together reach 2000 feet and are very barren of fossils. The latter 
contains beds of the peculiar Sylvania sandstone of the Ohio survey in 
which occasional fossils have been found — the only case on record. The 
minerals of the Lower Helderberg are celestite and calcite in pockets, 
and sulphur of which 200 l)arrels have been taken out within two years. 
The most valuable mineral is the salt of the Onondaga group of which 
3 beds exist near Detroit, the topmost at the depth of 800 feet, the sec- 
ond at 1200 feet and the third at 1800 feet. They have a combined 
thickness of 600-700 feet, including gypsum and shales interbedded. 
They thin away to the south and disappear within a few miles. 
The society then adjourned to meet next May ae Section E of the 
A. A. A. S. 
