DEMONSTRATION MATERIAL IN GEOLOGY 67 



submergence and emergence may be produced. In this tank deltas, wave-cut 

 and wave-built terraces, unconformities, mud-cracks, bubble impressions, and 

 other features are readily developed. 



"The glass tank has four drains situated at the bottom and at 2, 8, and 12 

 inches from the bottom. The glass sides and one end permit observation of 

 bedding and lamination and other features as they are being developed. In 

 (his tank may also be observed the contemporaneous deformation of sediments 

 while the deformation is taking place. A long, narrow glass tank is now in 

 process of construction in order to further study the contemporaneous defor- 

 mation of sediments. 



"In the trough the building of alluvial fans, the development of meanders, 

 the process of stream erosion and deposition are readily demonstrated. A fan 

 is shown in the trough in the right foreground." 



Geological Models 

 general discussion 



Many teachers of geology will probably be inclined to agree with one 

 successful teacher who states as his belief that "we are more in need of 

 good combined relief and structure models than any other material in our 

 teaching.' 7 There must, however, be at least one qualification : the models 

 must not be large. A model so large that it can not easily be handled is 

 soon discarded as a part of lecture equipment and is left to accumulate 

 dust. One reason that the models of Alpine structures sold by Kranz, of 

 Bonn, are so widely and effectively used is that they are of convenient 

 size. It is doubtful if models more than 3 feet long and 6 inches wide 

 are suitable for the lecture table, and shorter ones are even more desir- 

 able. It is probable that most teachers of geology have bought or have 

 made one or more geological-geographical models with the firm belief 

 that such reliefs would prove most helpful in teaching, only to find that, 

 because of the unwieldy character of the models, they could not be shown 

 to advantage in the lecture-room. In the geological museum of one of 

 our best universities there are on exhibition a number of fine geological- 

 geographical models, some of which were made at great expense. Never- 

 theless, but few of the students of elementary geology of that university 

 have seen them and still fewer have had them explained to them. This 

 is not an isolated example, but will apply to the geological relief maps of 

 most college and university museums. There is a real need for models 

 of North American structures. It is surprising that so few structural 

 models of this continent, suitable for class-room use, have been made, 

 notwithstanding the fact that models of parts of this continent are much 

 needed and illustrate common types of mountain structures much better 

 than the models of the Alps. 



