Algae reefs and oolites of the Green River formation

Reefs .or beds and is.olated n.odules .of fresh-water algal limestone are abundant in several parts .of the Green River f.onnati.on .of Wy.oming, C.ol.orad.o, and Utah. L.ocally they c.onstitute nI.ore than 8 per cent .of the basal InClnber .of the f.ormati.on and .occur in single reefs .or gr.oups .of reefs as much as 5.5 meters (18 feet) thiclc (See pi. 29, A.) O.olitic liInest.one and algal pebble beds are als.o plentiful but thinner. These algae reefs and .o.olitic beds are interesting n.ot .only because they nIake up an appreciable part .of the f.onnati.on but als.o because they indicate that the parts .of the lakes in which they and the ass.ociated beds were f.ornIed were shall.ow and clear except in times .of stonn, that the lakes had sheltered bays in which an emergent vegetati.on fi.ourished, and that the streams :feeding the lakes br.ought in a c.opi.ous supply .of dis­ s.olved calcium salts. It is also w.orthy .of passing n.ote that the algae reefs .of the Green River f.onnati.on, alth.ough f.ormed in inland lakes during the nuddle part .of the E.ocene ep.oeh, are rOInarkably similar t.o th.ose f.ound in the 11i.oeene lake beds .of the Rhine Valley in Germany. The SaIne species .of alga has been the chief agent in f.orming the reefs in each .of these tw.o widely separated l.ocalities, and, s.o far as the writer is aware, dep.osits with a c.omparable internal structure are elsewhere unkn.own.