144 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 64 



DESCRIPTION OF PLATE 17 



PAGE 



Greysonia basaltica Walcott. (See pi. 18) . . . '. log 



Fig. I. (Natural size.) Section of a mass of the basaltic-like columns 

 obtained by splitting ofif a group of the tubes. U. S. Na- 

 tional Museum, Catalogue No. 60713. 

 2. (Natural size.) View of the end of the basaltic-like tubes. 

 U. S. National Museum, Catalogue No. 60714. 



The algfe form the interspaces between the tubes that are now 

 filled with limestone. 



The specimen represented by figs, i and 2 is from locality 400c: 

 Algonkian : Newland limestone; 8 miles (12.8 km.) west of White 

 Sulphur Springs, Meagher County, Montana. 



