xl PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



parallel to this great circle will manifestly meet different meridians 

 at different angles, and, therefore, different lines of elevation coinciding 

 in direction with these small circles at different points of the earth's 

 surface, and consequently belonging to the same parallel system, must 

 be directed respectively to different points of the compass. The only 

 exception is presented in the system of which the equator is the great 

 circle of reference, in which case every hne of the system will meet its 

 meridian at a right angle, or will be directed exactly east and west*. 



I vdll now point out the steps we must take in their logical order, 

 to investigate the truth of this first part of M. de Beaumont's theory. 



We must first take all the lines of elevation with which we are 

 acquainted and divide them into two groups — the one containing all 

 those lines which can, on independent geological evidence, be referred 

 to distinct geological epochs of formation, and the other containing 

 those lines for which the evidence is inconclusive. Let the numbers 

 in these two groups be represented respectively by M and m. The 

 latter can afford us no fundamental proof of the trvith of the theory 

 we are discussing. 



The lines in the group M will form systems the number of which 

 will equal that of the recognized geological epochs of elevation, each 

 system being characterized by the contemporaneity of formation of 

 the lines composing it. We must now take each of these systems 

 and ascertain by the methods already indicated, the number of lines 

 in it which may be distinctly grouped into a parallel system. Let 

 the number of those, in the whole group M which can be thus 

 arranged in different parallel systems, be denoted by N, and let the 

 remaining lines in M be denoted by n. Then must the value of the 

 fundamental evidence in favour of this theory be found in the propor- 

 tion which the number N bears to n, or in the value of the ratio — . 



n 

 Let us consider its interpretation. 



Suppose the above-mentioned systems to occupy the surface of the 

 earth generally ; then if N be much greater than n, we must infer 

 that each of these systems of parallel lines is due to some cause, the 

 action of which has extended simultaneously to all parts of the earth's 

 surface, and which may be termed general, in contradistinction to 

 those causes whose action is local. It is to causes of this latter kind 

 that the other lines of elevation {n) are to be attributed. As an 

 example of a general cause, we may cite that of the shrinking of the 

 earth's superficial crust, resulting from that of its interior mass by 

 the loss of heat ; and volcanic action restricted to a limited space 

 affords an instance of a local cause. 



If n be much greater than N, there is no longer any distinct 

 indication of the action of a general cause in the above extended 

 sense of the term ; and the phsenomena under consideration must be 

 referred to mere local causes. 



If N and n be both considerable, our inference will be that some 



* All this will be made very obvious to the eye by simply placing a thread on a 

 common globe so as to form a portion of the arc of any great circle, and observing 

 the angles at which it crosses the different meridians. 



