1887] Methods of Instruction in General Geology. 62 3 
characteristic phenomena, describe them particularly, noticing 
the individual details, and endeavor to make the one case 
thoroughly understood in all its important relations, so that it 
becomes the illustration of the several principles involved. 
Thus, in explaining volcanoes, instead of spending the time | 
with an enumeration of statistics and formule, crowding the 
lecture with all the information possible about volcanoes, the 
whole lecture may be spent upon Vesuvius, its environs and 
history, making vivid impression of one or two typical eruptions, 
and, by the aid of maps of the region, pointing out the precise 
phenomena in the locality, sequence and results in building 
a cone and making volcanic deposits. With a-clear notion of 
one such typical volcano, it is a simple matter to classify and 
point out the kinds of volcanoes,—the pure tufa eruption, as 
at Monte Nuova, the continuous lava flow, as in the Sandwich 
Islands,—and by means of the grand eruptions recorded of Skap- 
tar Jokul, to gain a conception of fissure eruptions and the nature 
of the vast lava-fields covering now such large tracts of the sur- 
face, but without the conical mountain peaks which we naturally 
associate with igneous eruptions. 
In the same way in treating of river dynamics, instead of brief 
descriptions of the great rivers of the globe, the amount of their 
erosion and sedimentation, the volume and rate of their water- 
flow, etc., presenting a great number of condensed statistics 
. about many rivers, a better way is to spend the time in explain- 
ing the facts and their interrelations for a single typical river. 
No better example can be found for us than our great river 
Mississippi, so thoroughly studied and reported upon in Hum- 
d phrey and Abbott's monograph. For illustration of the principles 
: of erosion a familiar ravine, near by, is better than a large river- 
gorge at a distance. Niagara may well serve to illustrate the rate 
of erosion and as a short measure of geologic time. The cafions 
of the plateau district are illustrative of the laws of continuous 
depositions, of slow but great elevation, and furnish a longer but 
conceivable measure of time for geologic events. 
in all cases, where it is possible, selection should be made 
of a familiar and typical example, and around it should be 
gathered the details of facts and phenomena which will illus- _ 
- trate the principles discussed. By communicating a clear, de- 
tailed conception of the one example, the- indistinctness and 
