42 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 



THE HABITAT. 



The foregoing description, assisted by the profile (fig. 1), makes 

 it plain that superficially the distribution of the various communities 

 depends altogether upon the topographic factor slope. This of 

 course is a complex of simpler factors and the present study therefore 

 resolves itself mainly into an analysis of those factors whose variation 

 depends upon differences in direction and angle of surface inclination. 



At this point a summary of the observed angles may well be 

 given. 



Table 2. — Direction and angle oj slope. 



THE SOIL FACTORS. 

 Physical Chaeacteb. 



Samples were taken from a selected series of stations — Nos. 2, 3> 

 4, 6, 7, 10 — these being the ones used in the study of water-content- 

 From the first four, two each were taken, from 10 cm. and 30 cm. 

 depth respectively. In stations 7 and 10 three depths were sampled: 

 10 cm., 50 cm., and 100 cm. All of these correspond with the 

 depths used in moisture determination in each habitat. Since no 

 differences of moment were discovered between samples from a 

 single station, these have been combined and averaged in each case. 

 The analyses were made by Mr. Alfred Smith, of the University of 

 California, through the kindness of Dr. Charles F. Shaw. In the 

 first part of table 3 the five grades of sand and gravel have been 

 condensed into two. 



It is seen that the soils in all but station 2 are closely similar, 

 with the proportion of gravel and sand running from 77.57 to 

 83.66 per cent. Some, according to Dr. Shaw, would be classed as 

 light sands and others as sandy loams. Their similarity would be 



