In the southern Canadian Rocky Mountains the Mount Head and Etherington formations of the Rundle Group (Mississippian) contain abundant microcrystalline and pelleted limestones which some geologists believe were produced by zlue-green algae. There is little evidence, however, that such is the case. Rather do these limestones closely resemble modern carbonate sediments in the form of drewite and bahamites which are forming on the Bahama Banks through inorganic processes. The various bahamite grains recognized by Illing (1954) were identified in the pelleted limestones of the Rundle; namely, skeletal grains, faecal pellets, structureless grains, and composite grains.

Rarely observed filamentous molds, laminations, and algal pisolites suggest that the bue-green algae may have been locally abundant. No stromatolitic structures were observed.

It is concluded that the microcrystalline and pelleted limestones formed through inorganic processes in a shallow, warm water environment with restricted current movement, similar to that of the interior of the Bahamas Banks today.

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