GEOL. VOL. I.] SMITH SANTA CAT A LIN A ISLAND. 65 



IV. GEOMORPHOGENY. 



i. SUBMARINE TOPOGRAPHY. 



The submarine contours surrounding the island have been 

 represented for depths of 200, 300, 400 and 600 feet. The 

 discussion of the results arrived at by a study of this feature 

 of the topography has been left till this point, as these re- 

 sults are so closely connected with the geological history of 

 the island. By mapping in the deeper contours, it is seen 

 that the general form of the island is preserved to a depth 

 of at least 1,800 feet, and doubtless somewhat beyond this, 

 though the indications are that the pronounced trench out- 

 side Little Harbor gradually loses its character, so that at 

 some greater depth the outline of the entire mass may be 

 much simpler. 



In looking at the map it will be noticed that the average 

 distance from the shore to the 200 feet contour is much less 

 than the average distance from the 200 feet to the 400 feet 

 contour. This is particularly marked in those parts of the 

 island where the cliff cutting is the most rapid. By map- 

 ping in the contours on the large Coast Survey map of the 

 isthmus these features are strikingly brought out. Here, 

 since there is more detail, it is readily seen that the more 

 rapid deepening of the water near the shore extends to about 

 250 feet, and to this level the details of the present outline 

 are fairly well preserved. Beyond the 250 feet contour 

 there is a broad platform with a very gentle outward slope 

 (of about i) to some point beyond the 300 feet level. 



Beyond the 400 feet contour the water deepens rapidly 

 on the southern side of the island, while on the north the 

 widely separated contours indicate a gradual slope. The 

 pronounced difference between the two sides is well shown 

 in the accompanying sections (figs. 5 and 6) , which were 

 chosen as most fairly representing the average character of 

 the two sides respectively. The first is the section along 

 a line at right angles to the outermost point north of Whit- 

 ley's Cove; the other, along a line at right angles to the 



(5) January 12, 1897. 



