(j ANNALS NEW YORK ACADEMY OF SCIENCES 



Coastal Plain, and the Triassic Lowland are points all practically within 

 this area and within a day's travel of New York. 



The teacher of physiography in presenting the principles of the subject 

 to a class usually takes it up in a systematic way, dwelling first upon 

 the work of the various destructive forces which carve out the features 

 of the earth as the rivers, glaciers, waves, and wind, and then taking up 

 the great groups of land forms which are conveniently classified accord- 

 ing to their underground structure, the plains being those of simple 

 undisturbed and almost horizontal strata, and mountains those regions 

 of more involved character, distinguished by doming, faulting, folding, 

 complex metamorphic or crystalline rocks, and by volcanic action. 



WORK OF DESTRITCTIONAL FORCES 



Streams. — The work of streams is brought to the understanding of the 

 student by developing in a deductive way the life history of a stream 

 where drainage has been initiated by uplift of a land mass above sea 

 level. The different stages of youth, maturity, and old age are recog- 

 nized as depending upon the degree of adjustment which the stream has 

 acquired. The peculiarities which characterize each stage are noted, the 

 necessary new terms are introduced, and all of these constitute the data 

 of fundamental information which makes up this part of the subject. 



When the characteristics of a youthful stream are under consideration 

 the instructor calls to witness the rapids, the waterfalls, the narrow rocky 

 gorge of the Bronx River, its pot-holes, its swift current, and its pro- 

 nounced gradient, or he can go further afield and cite the swift brooks 

 of the Highlands, the Deerfield George in the New England Upland of 

 Massachusetts, or the mountain torrents of the Adirondacks. He may 

 cite the Niagara River system bearing the marks of youth in Niagara 

 Falls, the wonderful gorge, the racing current, and the interruption of 

 its course by the presence of lakes Erie and Ontario. 



The features of maturity are illustrated by -the upper portion of the 

 Bronx River, where it pursues a meandering course upon a limestone 

 lowland. An occasional abandoned meander may even be cited. Other 

 splendid examples are offered by the Wallkill River and its broad valley 

 in New Jersey and New York, arid among other streams which have 

 developed wide open courses upon the softer beds of the folded Appa- 

 lachians are the Rondout and Esopus Creeks. The Mohawk River in 

 part of its course is a mature stream. Some of the very finest references 

 to mature valleys, may be drawn from parts of the New England region, 

 notably in eastern New Hampshire and western Maine, where broad 



