Proceedings of the Polytechnic Association. 981 



"vvitli tlie boiler. The utility of such a contrivance is seen, when a 

 mass of flame or heated gases is passing along a flue, the exterior por- 

 tion, near the heat absorbing surface, becomes cooled, while the inte- 

 rior of the current retains its high temperature, radiation not being 

 sufficiently rapid to cool the whole uniformly. If then by any means 

 the current be broken up so that tlie hotter part of the gases is con- 

 tinually brought near the metal, the evaporative power of a given 

 amount of surface is greatly increased, thus producing economy of 

 fuel. To accomplish the same result without such appliances, the 

 amount of heating surface, and consequently the size and cost of the 

 boiler must be increased until surface is provided to absorb the heat 

 under the more unfiivorable conditions, ' ' 



On tue Geology of the South American Continent. 



Professor R. P. Stevens read a paper on this subject. Geologists 

 are at the present time divided into three great schools, viz : The 

 catastrophists, the evolutionists, and the uniformitists. "VVe leave out 

 of our count, those, if any, who still hold to miracles. 



Of the tliree great- schools, not one alone is able to explain all the 

 phenomena attending and connected with the growth of continents. 

 The eclectic geologist is the inner man, who selects from each and 

 all, and therefrom builds his theoretic structure. 



The first postulate I assume in the treatment of my subject is, that 

 there has been nothing new of material added to continents since 

 their first appearance above the surrounding oceans. 



The second postulate is, that the original material has undergone 

 changes in its aspect, and suffered new combinations, and been 

 removed and laid down in new localities. The continent of South 

 America presents the simplest form of continental growth and change. 

 It is therefore selected to present our views on the dynamic forces 

 which have formed great continental areas. 



The primary form of this continent, we think, was pretty much as 

 we now see it, viz : A great and somewhat irregular triangle. During 

 this stage of its history were laid down crystalline rocks. Such as 

 gneiss, mica and hornblende, slates, and intruded dykes of granite. It 

 is during this stage of its life that the theory of catastrophy will 

 apply to it. How else can we explain, that all rocks of this age over 

 the wide world, always stand upright. They bear internal evidence of 

 having been formed from pre-existing material, to have been laid 

 down on some level shore or ocean bottom, and afterward upheaved 

 and left in a more or less vertical position, never in a horizontal. 



