1 70 The American Geologist. March. 1905 
Thus, knowing that in tlie immediate vicinity of these 
caves there is a large deposit of gypsum, formed by the 
hydration of anhydrite, we must assign to this change the 
cause of the rock disturbances of the locality. Gypsum, 
however, is quite readily soluble in water, for according to 
Kohlrausch and Rose"^ one part of gypsum is soluble in 483 
parts of water at 15° C. That a very abundant supply of 
water is present to bring about the solution of the gypsum 
is evidenced by the fact that the level of the lake is reached 
at a depth of about 40 feet. This can be readily seen in 
several of the caves. 
The passing of gypsum into solution on a large scale is 
well known and may be observed in almost all gypsum 
quarries. \\ hen the mass of the mineral, thus removed, is 
of a considerable size, the overlying strata in many in- 
stances sink. Among others, Bischoff and Credner cite 
many such cases. Bischoff says, that oftentimes the rocks 
overlying gy^psum deposits first undergo uplift, folding and 
so forth and then as the mineral below is dissolved and re- 
moved these strata may settle, assuming a position nearly 
horizontal, thereby not revealing the fact that they had 
been disturbed at all. Credner* also refers to interesting 
phenomena at Eislehn, where conditions somewhat similar 
to those at Put-In-Bay exist. 
In the case at the Perry cave, we have had the folding. 
Solution has also taken place but not all of the overlying 
strata settled into a nearly horizontal position — some were 
left in the position they assumed as the result of the folding 
and now appear like an arch on a bridge or vault. 
The accompanying figure shows an ideal section 
through the Perry cave. Layers i and 2 show that the roof 
of the cave is still arched. Layers 3 and 4 represent the 
strata, which give evidence of a collapse for they do not 
extend continuously across the cave. The step-like ar- 
rangement of the strata at a and b conforms exactly to c 
and d in the roof. These, however, are not the only evi- 
dences of a collapse, for we often can note concave or con- 
vex unevenesses in the floor and directly above we find 
* Geologic 8te Auflage, 1897, 221, 222. 
