236 TEE POPULAR SCIENCE MONTHLY 



that lies between the subdued limestone range and the long radial 

 slopes of the volcanoes; perhaps they rise in lakes; but not until they 

 are all confluent is an outlet found across the broad and low saddle 

 between the third and fourth volcanoes; this being the lowest saddle 

 presumably because these two volcanoes stand farthest apart. There 

 the united waters of the rivers from the back country cut down a trans- 

 verse consequent valley roughly a hundred meters in depth, open it 

 to mature width, and prograde a simple cuspate delta in the sea beyond. 

 At the sides of the main valley, the spurs between the radial consequent 

 streams of the neighboring volcanoes are cut off by the river, and 

 frayed out by insequent wet-weather streams into small hills of similar 

 form and subequal height, consisting of tuff lying on the clays of the 

 prevolcanic lowland (or sea bottom), and here, with the subdued Sabine 

 range of the Apennines in the background (northeast) and the blue 

 waters of the Tyrrhene sea in the foreground, on a few of these frayed 

 out hills, not signalized otherwise from their fellows, the Eternal City 

 was built ; these hills are the Seven Hills of Eome. 



Three or four minutes may be required for this introductory state- 

 ment. The various specifications introduced in these few minutes — 

 subdued mountains of deformed limestones; large volcanic cones, with 

 calderas of engulfment replacing their original summits, and radial 

 consequent valleys submafurely dissecting their gentle outward slopes; 

 a consequent river, traversing the sag of a broad saddle between two 

 neighboring volcanic slopes, eroding a mature consequent valley, and 

 prograding a simple cuspate delta — all these specifications are easily 

 understood by hearers who are ready to listen to explanatory regional de- 

 scriptions. The relative positions of the several features may be indi- 

 cated by a blackboard diagram, or by a lantern slide made from a pen 

 and ink drawing, and are all so easily conceived that it is not really 

 necessary to point even once to the diagram as the successive elements 

 of the landscape are mentioned. At the end of the three minutes the 

 hearers will have grasped the essential features of the district about 

 Rome. Then a second and fuller statement of the same facts may be 

 begun, from which the hearers may learn that the limestones of the 

 Sabine mountains seem to be of subequable resistance, for the bare 

 domes of the subdued range have rounded forms of coarse texture, with- 

 out distinct exhibition of structural trends in the ridges or valleys; 

 that there are many small irregularities in the course of the consequent 

 valleys of the volcanic slopes, previously described as of radial arrange- 

 ment, a geometrical phrase that suffices very well as a first approxima- 

 tion to the fact, but which thus suiffices only because it serves as a good 

 beginning for a closer approximation; that the longitudinal river in 

 the depression between the limestone range and the volcanoes receives 

 three branches from the back country, the northernmost and largest bear- 

 ing the Tiber name to its head in the valleys of the central Apennines, 



