ANNIVERSARY ADDRESS OF THE PRESIDENT. Iv 



that these sudden movements would result from the cause here con- 

 templated, let us suppose the solid crust on the point of collapsing 

 under its own weight. If the crust were exactly spherical, of uni- 

 form thickness, and similarly constituted throughout, the tendency 

 to yield along great circles would necessarily be greater than along 

 small circles, but this tendency would be no greater along one great 

 circle than another. This exact uniformity, however, in the thick- 

 ness and constitution of the crust could never accurately exist ; and, 

 consequently, neither the forces tending to crush the solid crust, nor 

 its power of resistance would be strictly uniform, and in this irregu- 

 larity we have the cause determining the particular great circles 

 along which the yielding will take place. One of the simplest hy- 

 potheses we can here make is that of the crust being more feeble in 

 the region immediately surrounding a particular point, than else- 

 where. In such case the yielding would take place either along one 

 great circle, or simultaneously along several great circles, passing 

 through that point. The actual result would probably be that this 

 yielding would not take place continuously along each great circle, 

 but sometimes along one and sometimes along another, thus forming 

 a system of detached and separate lines of elevation of synchronous 

 formation, and characterized, not by parallelism to each other, but 

 by divergency from a point. These diverging lines might be formed 

 simultaneously in any direction whatever ; but let us suppose them to 

 lie between two great circles inclined to each other at a certain angle, 

 30° or 40° for example. We may conceive the yielding of the mass 

 and the consequent formation of longitudinal lines of elevation to be 

 continued far beyoird the region in which I have supposed them to 

 commence. For greater distinctness we may consider them to ex- 

 tend even to the point diametrically opposite that at which they 

 have originated, and where the great circles again intersect each 

 other. The portion of terrestrial surface lying between these two 

 bounding great circles is termed by our author a fuseau, — a term 

 adopted, I presume, as expressive of the fact, that the space to 

 which it is applied tapers to a point at each extremity ; and as far 

 as I can understand his meaning, he appears, in his physical reason- 

 ing, to consider that each collapse of the earth's crust would arise 

 from a simultaneous yielding along great circles of a fuseau, in the 

 manner above described. But there appears to me to be an incon- 

 sistency between such a view and the theory which asserts the con- 

 temporaneity of lines of elevation which are parallel to each other ; 

 for the lines of elevation formed as above supposed in the fuseau, are 

 divergent from the common point of intersection of the great circles 

 along which they range. 



It will be recollected that our author's lines of elevation in each 

 parallel system are portions oi great circles, but not of great circles 

 which meet in the same point. It is this latter circumstance which 

 characterizes ilao. fuseau — that space within which, according to the 

 above physical theory, a contemporaneous system of lines must lie — 

 in contradistinction to the zone of uniform width — the space which 

 must comprise a contemporaneous system according to our author's 



