88 £. B. Andrews on Peiroleum in its Geological Relations, 
is in some places divided into two parts by about two feet of 
soft shales, popularly called the “mud rock,” and the lower part 
is sometimes called the fourth nds rock. il is sometimes ob- 
tained in the mud rock. This is Marsa explained by the fol- 
lowing figure (fig. 4). A and B are the upper and lower divis- 
ions of the sand-rock; C is the ieee 
rock” penetrated by the well a. The 
shale is softened by the water in the 
well, and enters the well in the form of *+; 
mud. A small cavity, 5, is thus formed, 
which sometimes extends to an oil fis- 
siLees c, and thus a good oil well is ob- = 
‘At Tideoute, on the Alleghany river, 
a fine oil field, the famous Economite ‘ 
wells struck the lowest sand-rock about 
one hundred and forty feet below the sh ee “Very ae wells 
have been bored in the neighborhood without finding any lower 
sand-rock. I had little doubt, when examining the region, that 
this_sand- rock served the s me purpose as the third sand-rock 
ert retained in its fissures the oil. 
nomena of oil and gas springs were seen, Such ‘oil s rings first 
finds an outlet through fissures oe laterally to the 
surface of the outcropping rock. Whether by boring, at points 
remov om the outcrop, where there seta have been no sur- 
face drainage, large quantities of oil may be found, remains to 
en, it ‘sufficie ently capacious fissures in this oil-horizon 
exist, I have no doubt that they will be found to contain large 
quantities of oil. 
I would, in passing, venture to express my dissent from the 
opinion of some egies, that oil which may have been formed 
in higher strata descends to lower. In all my investigations of 
this matter I have never found any evidences of such a fact, 
while, on the other hand, the natural tendency of oil is upward: 
the waters lift it up; its cognate gases often force it up; the 
original oil vapors rise to condense in higher and cooler cavi- 
lower fissures may often be re-volatilized, to ascend an 
higher places of condensation near the surface. This last men- 
tioned process may have been going on in many regions for an 
