86 THE JOURNAL OF GEOLOGY. 



scheme ; but no amount of description suffices to place these 

 mental pictures before the class. The best means of overcoming 

 this difficulty is found in the use of the projecting lantern ; and 

 now that the electric light may be used in projecting slides on 

 the screen, and the room kept light enough for the class to take 

 notes while the pictures are exhibited and explained, the only 

 thing left to be desired is a good series of views, carefully 

 selected to present typical examples of land forms in various 

 stages of more or less complicated development. These views 

 are not intended primarily to furnish localized examples of geo- 

 graphical forms ; although, of course, they have much value in 

 that direction. Their greater value comes from the vividness of 

 the conceptions by which the different kinds of forms and differ- 

 ent stages of development of the deductive scheme are held in 

 the mind. The collection of slides that I now use includes a 

 large variety of views ; although wQ.xy useful, it is still imperfect. 

 It should be extended by the addition of many views taken 

 expressly to meet its needs ; for the photographs and slides com- 

 monly to be had of dealers are as a rule taken with anything but 

 geographical intention. As an indication of the character of 

 illustrations used in a single lecture, I may mention the follow- 

 ing examples, and add an outline of the comments made on 

 them. 



When the general idea of a geographical cycle has been pre- 

 sented, including the constructional forms with which it begins, 

 and an outline of the destructional forms by which its develop- 

 ment is characterized, the next lecture may be devoted almost 

 entirely to illustrations. First, a few slides to show various, 

 constructional forms. Muir's Butte, a young volcanic cone in 

 California, introduces a series ; it is practically unworn. Its 

 growth was so rapid and so recent that no significant advance in 

 its denudation has yet been accomplished. Mt. St. Elias comes 

 second ; as described by Russell, it is a constructional form 

 slightly altered ; an essentially young mountain mass. The 

 considerable time required for accomplishment of so great a 

 constructional work may have been enough for the slight dissec- 



