INTRODUCTION
3
Figure 1.—Representative microfossils, three-dimensionally preserved in chert from the Gunflint iron-formation of the north shore of Lake Superior. This formation is of middle Precambrian age and has been dated by K40-Ar40 as approximately 2 × 106 years. All figures are from thin sections of the chart photographed in transmitted light. Published here for the first time (from Dr. E. S. Barghoorn).
