Jan., 191 8. Annual Report of the Director. 



175 



Superior minerals which for a number of years had been loaned to 

 the Museum by the late Frank McM. Stanton was, owing to the 

 decease of Mr. Stanton, returned to Mrs. Stanton at her request. In 

 the space thus vacated, the collection of Chuquicamata, Chile, copper 

 ores, received during the year, and a series of BoUvia copper ores were 

 installed. By removal of less important specimens there were also 

 installed in this hall the series of gold and iron ores and accompan3ring 

 rocks from Brazil presented by Mr. George Chalmers, and a series of 

 specimens representing the ores of the Chloride, Arizona, district. In 

 order to provide greater security, the more valuable part of the platinuim 

 collections was transferred from this hall to Higinbotham Hall. This 

 has relieved the previously overcrowded condition of the case which 

 contained these specimens, and permitted better display of those of 

 less intrinsic value. In order to provide space for the exhibition of two 

 models which had recently been constructed, part of the synoptic fossil 

 collection was removed from Hall 35 and the models installed in the 

 space thus left. The models were constructed by the Assistant Curator. 

 One illustrates the processes of extinction of a glacial lake, the other 

 represents the relation of soil to rock in a glaciated region. The model 

 illustrating the extinction of a glacial lake was constructed to explain 

 the operation of those agents which are causing the gradual obliteration 

 of nimierous small lakes of glacial origin which are scattered through 

 the moraine belt of the country and are especially nimierous in parts 

 of Illinois, Michigan and Wisconsin. Incidentally the nature and origin 

 of the lake marl deposits are shown, as well as the mode of formation of 

 the peat beds of the Upper Mississippi Valley. These beds are some- 

 what different in origin from those commonly described in text books. 

 As it was found that no single lake was adapted to show these features 

 properly in a model of suitable size, the model was made as a composite 

 of a nvmiber of small Illinois and Wisconsin lakes with which the 

 Curators were familiar. The model is made of Portland cement rein- 

 forced with expanded metal. It is five feet long, nineteen inches wide 

 and two feet high. It was designed for installation on the floor of a 

 deep wall case. The scale is 30 feet to the inch, which is small enough 

 so that a considerable area can be represented and yet large enough to 

 show vegetation in some detail. On the upper surface, the model shows 

 half of a disappearing lake lying in a gravel and rock basin. The original 

 shores of the lake appear where the hills meet the swamp which forms 

 the present shore. From this original shore a swamp extends for a 

 considerable distance towards the center. The two ordinary characters 

 of shore marshes are shown in an open marsh of rushes and sedges on 

 one side, and on the other side a cedar and tamarack swamp. Beyond 



