and the Conditions which they Indicate. 19 



supplies the easterly rim of the sinking area, while on 

 the N. E. a submarine ridge connects New Zealand with 

 Australia, and supplies another segment of the margin. 

 The floor of this scallop-shaped depression is 15,000 feet 

 below the sea-level, and the focus of the last earthquake 

 shocks is located beneath an ocean 12,000 feet deep. Here 

 then we have the area of subsidence which this hypothesis 

 requires. 



If the recent shocks have been due to such conditions 

 as these, it would be likely that ruptures would occur 

 almost simultaneously at the depressed centre, and around 

 the mountain margin. If such has been the case it would 

 account for the apparently very high rates of speed, and 

 explain many discrepancies in the time-record, such as 

 the synchronous shocks at Wilson's Promontory and Beech- 

 worth, places on different seismal circles. 



I have stated that there are two other conditions under 

 which the earth's crust can be ruptured, and the surface 

 shaken. Both of these operations are superficial and local 

 in their effects, and both are connected with volcanic action. 

 The time at my disposal will not suffice to discuss their 

 applicability to the present case, and I will not stop to 

 describe them, as I consider that the conclusion best 

 justified by the phenomena recorded, is that the shocks 

 are due to secular shrinkage of the earth, this giving 

 rise to the fracture and distortion of the region about and 

 below us, with a depression of the sea-becl to the east of 

 Tasmania, and a slow elevation of the S. E. of Australia, 

 and perhaps the west coast of New Zealand. 



Art. IY. — The Atmosphere a Source of Nitrogen in 

 Plant Economy. 



By E. Lloyd Marks. 



TRead 11th June, 1885.] 



c2 



