5o6 ROBERT ANDERSON 



formed by a mingling of the products of eruptions and erosion. The 

 low slopes and hillocks where the plain rises into the wall are, as far 

 as observed, composed of lava both vesicular and conipact, and it is 

 most likely that the floor within no great depth below the surface is 

 composed of the same material. 



The floor of the caldera is everywhere cultivated, and supports 

 a population that may be roughly estimated as amounting to at least 

 5,000 people. Many villages and groups of dwellings are scattered 

 over the plain, and clusters of trees stand here and there. The 

 whole scene is a remarkable one, being especially brilHant when 

 the spring crops, which consist chiefly of green wheat and mustard 

 with yellow flowers are maturing. There is a legend that the moun- 

 tain-girt bowl of Aso was once occupied by a lake, until the god of the 

 mountain kicked a hole in the wall where the present outlet is and 

 allowed the water to flow out. There may have been in former times 

 flooded areas of more wide extent than those noted above, but it does 

 not seem probable that a real lake ever occupied the caldera. 



THE WALL 



The caldera has an oval shape and its rim forms a smooth sweeping 

 curve around the whole circumference, broken only at the cleft on the 

 west where the streams pass out, and on the east where the wall is 

 joined by the descending slope forming the extremity of the central 

 range. The curvature of the wall is so slight that it appears at a 

 glance like the face of a straight mountain range. On the basis of a 

 rough estimate it may be said that the average slope from the floor 

 to the top of the wall would nowhere exceed 25 or 30°, although 

 rocky almost vertical precipices occur at points on its face. The 

 wall is furrowed by gulches that have in places eaten back to the 

 summit and notched the skyline of the rim. In general, however, its 

 top is fairly even. Between the gulches sharp ridges run out into the 

 floor. The wafl varies in appearance from point to point, and the 

 ridges and prominences on its face have a variety of picturesque 

 shapes. The wall of the southern basin, exposed to the north, is 

 much more worn than that of the northern one. Forms resembling 

 the remains of terraces appear in places. The lower portion of the 

 wall has a gentle slope, and at some places is deeply soil-covered 



