NO. 6 



SMITHSONIAN EXPLORATIONS, I92O 



II 



nominal amount. Teeth of this species (Elcphas columbi Falconer) 

 are contained in our collections, but such a complete skull is of rare 

 occurrence, there being only one or two others in North American 

 museums. The specimen is further valuable in giving evidence as to 

 the proper position of the tusks in the skull, a subject of long 

 controversy. 



The second important exhibit secured during the trip was a slab, 

 measuring four by eight feet, of highly fossiliferous limestone from 

 the Richmond formation of Early Silurian age as exposed near 



Fig. 13. — Beginning of excavation for exliibition slab of Richmond limestone 

 near Oxford, Ohio. Photograph by Bassler. 



Oxford, Ohio. Such a specimen had long been desired for the 

 exhibition halls to show the advancement in life from the primitive 

 Cambrian forms, represented in the large Cambrian sea-beach sand- 

 stone exhibit, to the higher and more complex species of succeeding 

 geological periods, but notwithstanding the numerous occurrences of 

 fossiliferous limestone of Ordovician and Silurian age, it was not 

 until 1920 that a layer affording slabs of suitable size and sufficient 

 perfection of preservation was brought to the attention of the 

 Museum. This was discovered by Dr. W. H. Shideler, Professor 



