Stromatolites reached their acme during the late Precambrian, after which they went into a slow decline, possibly due to the appearance of more highly evolved algae and Metazoa, or when snails evolved, which feed on algae.



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Geographical distribution
The geographical distribution of stromatolites is vast. The earliest structurees date frome more than three billion years ago, and there are major calcareous deposits still in the process of formation, due mainly to the action of algae; among the most important examlpes are those in the marshy Everglades of Florida and the marine stromatolities in Shark Bay, Western Australia. The Photograph shows the cross section of stronmatolite of the genus Jacutophyton; this particular specimen comes from Mauretania and dates from the Upper Precambrian (700 million years ago).
Copyright 1986 by Arnoldo Mondadori Editore S.P.A.,Milan. Simon and Schuster/ Fireside BOOKS "Guide to FOSSILS"