44 
IOWA ACADEMY OP SCIENCES. 
this natural gas contained in its water supply may yet furnish 
Perry with a convenient fuel. 
In the case of the wells near Letts, Louisa county, the con- 
ditions appear to be slightly different. They have a depth 
ranging from 90 to 125 feet, but do not reach the base of the 
drift, since in a number of iu stances the rock in this 
region has not been struck at 280 feet below the surface. 
“ At a depth of from 6 to 25 feet below the gas a good, constant 
supply of water is obtained. It seems to be very easy to shut 
off the gas by the rapid sinking of the casing in a sort of blue 
clay with some sand, in which the gas is thought to be stored. 
The clay seems to form a tube as the drill and casing descend, 
and this prevents the gas from getting into the well unless it 
is given a little time at the right place. The country for miles 
around is full of wells which are all believed to be sunk to the 
water below the gas, without discovering the latter for reasons 
given above.” Prom the foregoing statements it is apparent 
that the gas at this locality does not occur in a well defined 
sand bed, but is distributed through the upper portion of the 
Pleistocene deposits, being usually found at a depth of about 100 
feet. There seems to be abundant evidence of the presence of 
extensive accumulations of vegetable material in the drift of 
this region. 
But Iowa is not the only state where natural gas is found in 
the surface deposits, for it occurs also in the drift of Ohio, 
Indiana and Illinois. Its occurrence in Ohio is mentioned by 
Orton.* On the southern margin of the drift of that state and 
for twenty to forty miles back from its border there are in many 
parts of the state considerable accumulations of vegetable matter 
covered by later deposits of the drift period. Wells dug into 
these deposits often strike quite extensive accumulations of one 
or the other of the two gases given off by the decomposition of 
this buried vegetation, namely, carbon dioxide and marsh gas. 
Sometimes carbon dioxide, or carbonic acid gas as it is com- 
monly called, is found in all the wells of the neighborhood and 
no water well can be completed on account of its presence. It 
is not an uncommon thing for well diggers to lose their lives 
from this deadly choke damp.” 
Calvin has noted several instances in Iowa where this gas 
escaped with considerable force from holes bored for water. 
*Geol. Surv. of Ohio, vol. VI, pp, 773-775. 
