Michigan Gypsiim Deposits- — Grimslcy. 383 
upper series outcrops alonj:^ the river in the city nearly to its 
north limits.* A number of quarries have been opened in the 
bed of tlie river, and, according to Rominger, the contact, could 
be seen at the foot of the rapids in the earlier history of the city. 
This limestone is about 50 feet thick. 
The only localities in Michigan where gypsum is found in 
this formation near the surface, are in the vicinity of Grand 
Rapids and at the east near Alabaster. The formation, how- 
ever, is found in a belt of varying width bordering the coal 
basin, and through most of the area it is more or less concealed 
by the overlying drift. 
QUANTITY OF GYPSUM IN THE ANCIENT MICHIGAN SEA COM- 
I'.VRED WITH THE PRESENT SUPPLY. 
The area of rocks in Michigan after the Marshall or Kin- 
derhook series is approximately circular in outline with a rad- 
ius of 85 miles giving an area of 22,686 square miles. As will 
be shown later the sea covering this area in Osage times was 
approximately '700 feet in depth and assuming an average depth 
of 326 feet, based on well records, there would Have been about 
1,280.000 billion gallons of water. 
The analysis of Atlantic ocean water shows 93.3 grains of 
gypsum to the gallon. If this Michigan sea had this same pro- 
portion, it would have yielded 8,500,000,000 tons of gypsum. 
The thickness of gypsum at Grand Rapids is 18 feet and at 
Alabaster 20 feet. The approximate area at Grand Rapids is 
24 square miles and at Alabaster 10 square miles, and while the 
gypsum does not by any means keep the thickness given over 
the entire area and is even absent in places, it has probably been 
removed by solution since its deposition. 
These figures would give a total quantity ol 1,237.764.000 
tons of gypsum. Where gypsum is found in the deep wells it 
is usually in thin beds and in many of them it is entirely absent. 
It is thus evident that the quantity of gypsum held in this old 
Michigan salt sea is sufficient to explain the quantity of gypsum 
actually in existence today in its basm. 
If the assumption is made, and there is no basis for it, that 
the gypsum covered all the interior sea area with a thickness of 
20 feet, then it would require 917 billion tons of lime sulphate in 
* See Whittcmore Prbc. Micb. Acad, of Sciences. Also StronK. Proc. Keat 
Sci. Inst. No. 3. 
