Although an element of skepticism has traditionally prevailed, on the part of both geologists and biologists, with regard to the existence and nature of Precambrian life, evidence is now rapidly accumulating which supports the view that widespread and abundant biological activity occurred as far back in the geologic record as half the presently accepted age of the earth. Geochemical evidence and evidence from the mineralogical and petrographic characteristics of Precambrian rocks is equivocal regarding the time of origin of life and the physical setting of biogenesis. However, structurally preserved fossils showing well-defined morphology are now known from sediments of an age approaching 2000 million years (1, 2). It is the purpose of this article to discuss the geologic occurrence of these oldest known Precambrian fossils, their morphology, and certain chemical analyses of the extractable organic residues. Detailed study of hundreds of thin sections has demonstrated a complex of biologically variable morphological entities. From the range of structures examined, eight distinct generic categories have been selected for detailed description.Dr. Barghoorn is professor of botany in the department of biology and curator of Paleobotanical Collections, the Botanical Museum, at Harvard University, Cambridge, Mass. The late Dr. Tyler was a professor in the department of geology at the University of Wisconsin, Madison. FEBRUARY 1965Twelve new species are these range from single-celle spheroidal bodies to fi branched and unbranchec Among these forms are rat plex, highly distinctive orga unusual morphology and phylogenetic affinity. With preserved units of the cher ganisms occur in profusion.No attempt is made here the voluminous literature on brian fossils. This has beer and excellently done by Gla and Rutten (4). General GeologyThe term algal cherts has applied to certain facies of flint iron formation of the Lake Superior region of Ca adjacent Minnesota. The Gu: formation is one of two S1 conformable units, of which shale is the overlying men gether the Gunflint and the 1 prise the recognizable Anim in the Thunder Bay District o The termn A nimikie rati Huronian is used here becal lack of direct stratigraphic ( with the classical tripartite sequence in the Lake Georgean Bay area to the absolute age of the Gunflint formation is approximately 2000 million (2.0 X 10?) years (5), and this age places the formation in the lower third of the Middle Precambrian.The Gunflint sediments extend eastward some 175 kilometers from the vicinity of Gunflint Lake, on the U.S.-Canada boundary, to Loon Lake, Ontario (Fig. 1). Isolated remnants of the formation occur on the mainland and upon islands in Lake Superior in the Rossport-Schreiber area some 98 kilometers east of Loon Lake. In the Gunflint sequence of Minnesota four major members may be distinguished: Lower Cherty, Lower Slaty, Upper Cherty, and Upper Slaty (6). In many exposures of the formation, however, described; one or more of the upper members has d isolated been removed by ...

Considerable progress has been made in the improvement of technics of preparation and identification of mineral species present in the colloidal fractions of soils and sediments, particularly of montmorillonite and the micas, through the x-ray diffraction method. -1s a result, considerable information Joint contribution of the JTisconsiii Agricultural Csperinient Station and the Dcpartment of Geology, University of \Tisconsin, Madison. Putdished by peiiilisoioil of the Director of the Agiiculturnl C\perimeiit Statioji Supported in part by a graIlt fronl the Wisconsin .4lurntii Re-earch Toundation.2 It is considered essential, however, t h a t the clay-size inirierals be studied in narrow particle-size ranges such as the three listed, for b o t h theoretical and experimental reasons. Moreover, thc limits of these arbitrary sizc i'ariges arc also Eunctiorial in character, rather than unique numerical limits.3 Collectioiis obtained though the courtesy ui Professor A , Scott, Lava1 University, S t . Anne tie la l'ocatih?, Quebec, Canada.

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