39 6 



University of California. 



[Vol. i- 



force or lessening the resistance, will cause these movements to go 

 farther than they otherwise would. This is but an example of 

 reaction of effect on cause, of which we find so many in all cases 

 of complexly related phenomena. As to the real and fundamental 

 cause of the oscillatory crust movements we are not yet prepared 

 to speak with any certainty. We must wait for more light."* 



McGee, in i888,t refers to subsidence by loading, but says that 

 it is a process which would soon run down were there not other 

 forces active to revive it. 



Prof. Lloyd Morgan, J in the same year, suggested a rather novel 

 view of the cause of subsidence of the earth's crust under a load of 

 sediments. He supposed that the weight of the latter might solidify 

 a portion of the underlying fluid magma which would then contract 

 and allow a certain subsidence to take place. Furthermore, the 

 solidified portion, by sticking to the bottom of the crust, would 

 tend to increase the weight and carry the process further. Where 

 it would finally stop we are not told. 



Ricketts, in 1 889,$ argues that subsidence is due to loading by 

 sediments, but the most interesting thing in his paper is a foot-note, 

 in which he states that he has seen at least ten instances where the 

 Carboniferous limestone, during the period of its formation, had 

 been locally raised above sea-level and eroded. In eight of the 

 examples thin beds of coal were found on the eroded surface,, 

 sometimes separated by clay. Just how this evidence supports his 

 general contention is not by any means clear, while it certainly is 

 very welcome to those opposed to it. 



In 1889, Dutton|| conferred a great service upon the hypothesis 

 first advanced by Herschell, by casting it in a more comprehensive 

 and clear-cut statement than had been done hitherto, and by propos- 

 ing the word isostasy to express that "condition of equilibrium of 



' : Loc. cif., p. 180. 



t Some Definitions in Dynamical Geology, Geol. Mag., Vol. XXV (1888),. 

 P- 493- 



jGeol. Mag., Vol. XXV (1888), p. 291. 



'i On Some Physical Changes in the Earth's Crust, Geol. Mag., Vol. XXVI, 

 p. 47. 



|| On Some of the Greater Problems of Physical Geology, Bull. Philos. 

 Soc. Wash., Vol. XI, pp. 51-64. 



