6 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



the main ridge bounding Avalon Canon on the west; (2) 

 the ridge connecting the main ridge with the point north of 

 Whitley's Cove; and (3) a portion of each of the ridges 

 running from the main ridge into the Little Harbor region 

 (which comprises the semicircular area within a general ra- 

 dius of about three miles from Little Harbor). 



In the lower portions of the Little Harbor region this sec- 

 ond type of topography again appears. Within this area 

 the tributary ridges, radiating from a central point not far 

 from Little Harbor, rise to the higher slopes by a long, 

 moderate incline. Beginning at the shore-line, with a cliff 

 of from 200 to 300 feet, the rise above this is very gradual, till, 

 at an average distance of a mile and a half from the water, a 

 height of about 600 or 700 feet is reached. Beyond this 

 the grade increases, and an altitude equal to that of the main 

 ridge is soon reached, usually some little distance from the 

 main ridge itself. Standing on the lower and more level 

 portion of this area, and looking either toward the isthmus 

 or in the opposite direction, one sees a great amphitheater, 

 the distant ridges rising one above another, like gigantic 

 tiers of seats, up to the main ridge. Were it not for the 

 recent stream erosion we should thus have in the immediate 

 neighborhood of Little Harbor an almost even surface, with 

 a gentle seaward slope. The present drainage, however, 

 has dissected this surface, cutting channels some of which, 

 in their lower stretches, have a width of 100 yards or more, 

 and a depth of perhaps 200 feet. In places the streams 

 have made considerable deposits, and at a number of points 

 these have been cut through, in very recent times, to a max- 

 imum depth of about twenty-five feet, at some distance from 

 the shore. 



Slope of Summits. — It has been seen that the main ridge 

 and certain of the branch ridges are, in a general way, level 

 in the direction of the length of the island. In those por- 

 tions of the main ridge on either side of Avalon Canon 

 which are oblique to the trend of the island, the generally 

 level summits are seen to slope at an angle of a little over 



