1894. CONTINENTAL GROWTH. 343 



This will be due mainly to the persistence of the physiographic 

 features of the land-areas, which will only change when the internal 

 forces of the earth, reacting on the sedimentary mantle, develop 

 expansion therein, and by lateral and vertical pressures and move- 

 ments oftentimes renewed, develop those ridges of the earth called 

 mountain chains, and so diversify the planet's surface by sketching 

 out new land-surfaces where now is sea, thus modifying the form and 

 conditions of the old continents. 



General Conclusions. 



The result of our reflections upon the group of facts which it has 

 been the object of this paper to bring together in systematic order 

 tends to show that the growth of land-areas of the globe is governed 

 by certain laws of development. The records of the rocks tell us 

 pretty plainly that there must, throughout geologic time, have existed 

 land-areas on the globe comparable in extent with those now existing. 

 It is not my intention to touch upon that vexed question, the 

 permanence of ocean basins, or to sketch out the lines of former land- 

 extensions. We have seen that land-areas grow by accretion from 

 existing land. The ruins of former continents have added to their 

 extent, so that by process of accretion their outlines and physiographic 

 features have altered ; therefore, the present continents, though the 

 outgrowth of earlier ones, may be vastly different in form, position 

 and orography from their predecessors. That the land-areas should 

 have been preserved through geologic time, considering that their mean 

 heights are so little above the water, has always presented itself to my 

 mind as a geological crux. We now see that the waste of the land 

 and the collection of the resultant sediments in the bordering seas is 

 Nature's means of renewal, and we further gather that continuity of 

 land-areas throughout geologic time, so necessary for the preservation 

 of terrestrial life, is in this way secured. The origin of mountain 

 ranges and the growth and decay of continents are thus closely 

 related. New lands are the consequents of sedimentary loading and 

 recurrent expansion, acting through a chain of events which I have 

 dealt with in the" Origin of Mountain Ranges," and which seem to 

 me to be the explanation which brings together all the hitherto isolated 

 facts of geology into one comprehensible whole. Our planet's history 

 is not one of fortuitous accident, but of development by law, and, as 

 I believe, in the manner herein of necessity slightly and concisely 

 sketched out. 



It is through the labours of many geologists gathering facts 

 out in the iield in both hemispheres that we are enabled to approach 

 the subject with any probability of a reasonable solution. As these 

 facts accumulate we shall be in a better position to test, modify, and 

 develop our theory. In the meantime, I have reasonable hopes that 

 this outline may form a not unsuccessful guide in directing future 

 investigators towards a true explanation of the earth's geologic 

 vitality. T. Mellard Reade. 



