The James M. DuPont Meteorite Collection - They were the Hmestone building organisms of the Proterozoic and Early Cambrian. With the appearance of limestone building animals in the Cambrian and Ordovician their importance decreases greatly, but they have continued in considerable numbers down to the present day. However, in morphology and structure, they show practically no change after Late Cambrian times, consisting of mats or felts of tiny algal filaments which often trapped some silt or organic debris and was encased in a mold of fine cal- careous dust precipitated by the algae. Commonly they developed colonies of a consistent shape, show growth laminae, but little or no microstructure. Bibliography Doty, MS 1957. Fxology of marine Algae (annotated bibliography). Treatise on marine ecology and paleoecology.
http://www.youtube.com/watch?v=pskebf7Ojbc&hl=en
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