E.— GEOGRAPHY 



itg 



The factories alternate on the west with large areas of wooden or brick 

 houses occupied by foreign labourers. 



The heavy broken lines (linking the four stages in Fig. 14) indicate 

 the gradual growth of the city. Obviously this growth (as shown in 

 Fig. 14) resembles a cone, starting at the original humble houses of the 

 first settlement and gradually expanding (as a ' small-house zone ') on 

 all sides as time progresses. The later type of building can also be 



se-rreff looses l.i."| 



Fig. 14. — A ' Zones and Strata ' Diagram Showing the Evolution of Chicago for 



Eighty Years. ^ 



Notice that the older types of structure now occur on the periphery. The 

 (skewed) squares are four miles across. The heavy broken line linking the 

 four diagrams indicates the spread of the outer zone of simple wooden houses. 

 (C/. Fig. 15.) 



represented by such conical growth-forms. The phenomenon is much 

 like the series of concentric craters built up by the lavas in a gradually 

 increasing volcano. Each lava-flow may be supposed to cover part of 

 the preceding flow, but to push some of the mobile earlier lava still farther 

 to the periphery. The whole concept as applied to culture-spreads has 

 been illustrated in Fig. 12 earlier in the address. 



Since these ' craters of growth,' as I have named them, help us con- 

 siderably in our search for affinities of isolated tribes, speeches or cultures, 

 I have developed the concept somewhat further in the next diagram 

 (Fig. 15). Here the second ' crater ' illustrates how the Mediterranean 



