24 THE PALEONTOLOGY OF MINNESOTA. 
[Discovery of microscopic bodies. 
value as well as of scientific interest. One of which, while not quite germane to the 
subject under consideration, we will mention as an illustration. When the “lake 
tunnel”, which supplies the city of Chicago with water from lake Michigan, was in 
process of construction, in 1865-1867, large numbers of minute and nearly trans- 
lucent amber-colored discs, 4, to ;4, of an inch in diameter were discovered by two 
members of the Chicago Academy of Sciences, in the clay through which it was 
being driven, at a depth of about 86 feet below the surface. These discs were 
unknown to paleontologists, to several of whom they were submitted. Careful and 
repeated examinations showed that the whole mass of the boulder clay underlying 
the vicinity of Chicago was loaded with these discs, and also that the many frag- 
ments of shale and shale boulders in the clay were largely composed of them. This 
last discovery rendered it more than probable that the discs in the clay were derived 
from the shale, large formations of which must at some period of the world’s history 
have been broken up and scattered through it.(‘) The shale when lighted by a lamp 
or candle burned freely with a smoky flame and strong petroleum odor. Our next 
light was from a paper by Sir William Dawson, published in the American Journal 
of Science in 1871, in which he stated that similar “microscopic orbicular bodies” 
had been referred to by Sir W. E. Logan, in a report in 1863, as occurring in the 
“Upper Erian shale” at Kettle point, lake Huron, and to which he (Sir William) 
gave the name Sporangites huronensis(*), the two principal species of which are 
now known as Protosalvinia huronensis Dawson, and P. chicagoensis Thomas. Prof. 
Edward Orton, state geologist of Ohio, in a report on “Petroleum and Natural Gas”(’), 
after referring to the great fishes, &c., as described by Newberry, and other fossils 
of the oil and gas producing shales of Ohio, says: “But the forms already named 
are of small account so far as quantity is concerned when compared with certain 
microscopic fossils, that are of little doubt of vegetable origin, and which are accu- 
mulated in large amount throughout the black beds of the entire shale formation, and 
apparently give origin to an important extent to the bituminous character of the 
beds. * * * They were first discovered by B. W. Thomas, a Chicago microscopist, in 
the water supply clay and shale at Chicago’’(*) * * * “The thickness of the series of 
shale now under consideration is, in Crawford county, about 450 feet, in Loraine 
county about 950 feet, at Cleveland 1,350; while in Tuscarawas county the drill 
reached 1,860 feet, and in the Ohio valley at Wellsville, 2,600 feet in shale without 
reaching bottom.” On pages 413 and 414 of the same work, under heading of “Ohio 
Shale as a Source of Oil and Gas”, Prof. Orton says that “they contain much more oil 
(1) Bulletin, Chicago Academy of Sciences, No. 4, 
(2) Bulletin, Chicago Academy of Sciences, No. 9. 
(3) Geological Survey of Ohio, Vol. 6, 1888. 
(4) As stated above, they were first discovered by Sir W. BE. Logan, but he gave them no further notice. 
