No. 65: Sep-Oct 1989
"Geologists have discovered strange disc-shaped features in slate deposits in California. The features, at Yreka, are between 2 and 7 centimetres across and 2 to 4 millimetres thick; some have centres stained with iron oxides. One geologist, Nancy Lindsley-Griffin of the University of Nebraska, has already dubbed the saucer-shaped features, 'unidentified fossil-like objects.'
"Geologists discoverd the UFOs in bedding planes of the slate, formed from ocean bottom that was deposited between 400 and 600 million years ago. The objects are puzzling because they lack the symmetry that fossils of living organisms usually display. They are also too large to be the droppings of any creature alive at the time, and do not look like concretions, such as agates, formed by natural chemical processes. Lindsley-Griffin says they resemble very tiny bicycle wheels, with a central core and an outer rim, but with most of the spokes missing.'"
One thought is that these features may be fossil jellyfish.
(Anonymous; "Fossil 'UFOs' Mystify the Geologists," New Scientist, p. 43, July 1, 1989.)