206 Field Museum of Natural History — Reports, Vol. X 



proved more economical of space, and several hundred additional 

 specimens were placed on view. A new exhibit, consisting of speci- 

 mens collected by the Marshall Field North Arabian Desert Expedi- 

 tion, was installed in this hall to illustrate the destructive action 

 of the sun on rock surfaces. The collection illustrating such surface 

 desert phenomena as desert varnish, sand polish, and erosion by 

 wind-blown sand, was revised and greatly enlarged by the addition 

 of specimens from the Marshall Field North Arabian Desert Expedi- 

 tion and the Marshall Field Brazilian Expeditions. The exhibits 

 of claystones and barite roses were enlarged by the addition of 

 specimens received during the year. 



Work on the collections in Frederick J. V. Skiff Hall (Hall 37) 

 was confined to such cleaning as was necessar^^ and the addition of 

 a few specimens received during the year. The appearance of the 

 hall has been improved by replacing 1,743 of the old black labels 

 with new buff labels matching the background of the cases. The 

 collection of unusual zinc and lead ores from Embreeville, Tennessee, 

 was installed in a case formerly occupied by a collection of zinc 

 ores from Greece, now transferred to another part of the hall. The 

 new collection, which occupies a whole case, is unusually attractive 

 because the specimens take the form of cavern deposits such as 

 stalactite and stalagmite. 



Two large blocks of the potash ores of New Mexico are an 

 important addition to the potash collections, as they show the nature 

 of this deposit better than the drill cores formerly shown. 



In Ernest R. Graham Hall (Hall 38) fossil skulls of the saber- 

 tooth tiger, Smilodon, the Andean horse, and a giant turtle were 

 added to the collections. Further changes were confined to minor 

 readjustments such as replacing inferior specimens, and rearranging 

 specimens that were not in proper geological sequence. 



Preparation of specimens for exhibition continued through the 

 year in the laboratories of vertebrate paleontology^ The working 

 force of this laboratory was increased during part of the year by 

 the re-employment of Mr. James H. Quinn as preparator for eight 

 months, and by the attachment of Mr. Robert Witter as volunteer 

 helper for four months. Specimens prepared for exhibition, and in 

 process of preparation, in these laboratories, while few in number 

 are of great importance. A skeleton of the large South American 

 mammal, Astrapotherium, has been reconstructed from a poorly 

 preserved specimen and for the first time the entire bony structure 

 of this rare animal has been shown. Another rare skeleton, of a 



