24 THE PALEONTOLOGY OF MINNESOTA. 



LUiscovery of microscopic bodle*. 



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, T V to 7 ^ir f an i ncn i n 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.( J ) 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 Brian shale " at Kettle point, lake Huron, and to which he (Sir William) 

 gave the name Sporangites huronensisC*), 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- 

 mulaled 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".( 4 ) * * * " 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 Tuscaravvas 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 "Uhio 

 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. 

 <2i 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. E- Logan, but he gave them no further notice. 



