18 Indiana Natural Oas Field. — Leverett. 
county, Montpelier, Blackford county, Camden and Portland, 
Jay county. On the north and west the gas fails near the line 
where the limestone begins a rapid descent. Where the sur- 
face of the Trenton is 100-120 feet below tide it is unusually 
saturated with water. The question of altitude is therefore the 
all-important one on the north and west borders of the gas 
field. At the southeast the limits of the gas field are less clear- 
ly defined than in other directions. Here the failure of gas is 
not due to a decrease in the altitude of the Trenton and conse- 
quent swamping by salt water ; on the contrary the altitude is 
greater as a rule than in the productive district. It is due to 
a change in the texture of the gas yielding rock. Prof. Orton 
discovered this fact on the southern borders of the Ohio gas field.' 
He found a granular, porous, dolomitic limestone containing 
but a small amount of insoluble material to characterize the 
productive gas field, while a less porous limestone containing 
but little carbonate of magnesia, but having much insoluble 
material, characterizes the unproductive portion of the Cin- 
cinnati anticlinal. It is the physical structure of the rock, not 
its chemical composition, which determines its capacity to 
contain gas. As might be expected, this change in texture has 
an irregular border, and is more complete at some points than 
at others, consequently it is difficult to define the limits of the 
gasfield on the southeast. The strong gas wells lie north of a 
line connecting Greenfield, Muncie and Red Key, Jay county. 
Weak wells are found at various points in the southeastern 
counties of Indiana. 
Strength of lo ells. — Many of those classed in the tables as 
good gas wells yield less than 1,000,000 cu. ft. per day, as their 
capacity to furnish fuel clearly shows. Not infrequently wells 
are found to yield when piped for fuel no more than half the 
amount indicated by the gauge. There are within the territory^ 
however, wells which yield not less than 7,000,000 cu. ft. per 
day. Such are the "Jumbo" well at Fairmount, in Grant coun- 
ty, and the "Granger'^ wells near Noblesville, in Hamilton 
county. There is often a great difference in strength display- 
ed by wells in close proximity, the variation being probably 
due to difference in the texture of the rock. 
Minor anticlinal. — Near the line of Tipton and Clinton 
' Geology of Ohio; vol. vi, pp. 103-105. 
