70 
REPORT- 1847. 
been put forth respecting contemporaneity in the former sense is that of M. 
Elie de Beaumont, according to which all chains of mountains parallel, in a 
certain sense, to each other, are regarded as being of contemporaneous 
origin. I am not aware however that any physical cause lias been assigned 
for the geometrical law which this theory asserts, and consequently the 
examination of tlic theory docs not lull within the province of this Report 
Restricting ourselves to limited areas, wc may define as a dUtinct district, 
any area throughout which the phamomt-na of deration are connected by a 
continuous geometrical law; and the theory which has lK*en developed in 
this section would assert that that elevator}' movement, or those successive 
movements which impressed on the phamomcna tliis continuous law, niuai 
have been contemporaneous tliroughout the whole district Wc have seen, 
in fact, that the primary fissures must bear certain relations to the form of 
the area contemporaneously elevated; and therefore, if a whole elevated 
district were upheaved in separate portions at ililferent times, the primary 
fissures could not be groupiid according to the same continuous law as if 
the whole district had been elevated contemporaneously. 
Ihe question of contemporaneity, with respect to vciiical elevation, is one 
of more diflicult dctcrniinatiou. There aro probably few geologists disposed 
to advocate the extreme opinion that the elovation of each disturbed district 
has been effected by one single upheaval, or the opposite opinion, that it has 
^en the result of an imlcfiuito number of almost infinitesimal movenieDls. 
The question may rather be stated to be, whether the existing elevation lias 
been jiroduced by a email imnibcr of comparatively great and decisive 
movements, or by a greater though not an iiulefinite number of smaller ones. 
In discussing tliia question, lot us in the first place suppose the clevatory 
movement to have been sultieieut to ujilift the mass a little beyond llict 
height at winch the primary fissures would be formed. We shall then have 
the case represented in fig. 3. After the coUapso of the dislocated mass, the 
cUtterent portions would be maintainerl by friction in their new relative poai* 
tions. VVhen another uphi'uval took place a similar effect would be produci^, 
t ie relative displaceracuts being increased at each successive upheaval; auil 
observed amount of verUcal displacement nmy be as easily con¬ 
ceived to have been the result of a groat number of sroaller displaccnienti, 
^ number of greater movements. In the same manner equal 
. 1 ‘"to action, mid therefore equal relative 
Thp"Si in both these modes ofdcvatioa. 
hori 7 lf.o„rJ‘"i “ ^‘^Placcment, in addition to those which are vertical or 
that r ^ <iwfni>ted mass could receive, would ba 
BnmVZolL lT'm'^ moyemenL Now at each small upheaval a 
‘n fiR- in being very small. But here it must be 
forces i «ulisidcnce of the mass, the horuoutal 
coSuems is?/, explained, would exert on enormous power to restore 
to each othlT An 1*^*1 • migular positions relatively 
and thQuretio.*'^ ^'•‘'at Uifflrence between this case 
be al cIlLtiveTn^’nrl"' necessarily called into action would 
they would be in S ®ncces8ive small vertical displacement, as 
are^norcmirid/inr^^^^^^^^^ displacement in the case wc 
great, we have seen Vart' ar"? 'bsplaeement should be sufficiently 
oven no tendenev it. ii \ b.) that there might be only a small tendency, or 
position • but that v 'i restore the displaced mass to its original angub^ 
i^hould be BuiaJ er become greater as the angulw disturbant’C 
*« be smaller; and hence, the probability that a great tngular dUplacc* 
