26 



SMITHSONIAN INSTITUTION 



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Fig. i8.- 





-Cliffs of pre-Cambrian limestone along Little Birch Creek, Belt 

 Range, Montana. (Photograph by Resser.) 



I'K.. ii>. — Clil'l'^ n\ pre Laiiiljrian limestone, and camp almi^; Little Birch 

 Creek, Belt Range, on the Ringling ranch, west of White Sulphur Springs, 

 Montana. In 1914 Dr. Walcott shipped in many tons of algal limestone 

 collected in these cliffs. (Photograph by Resser.) 



