182 Proceedings of the Royal Society of Victoria. 



ances of an extraordinary character during the [Post Tertiary] 

 period, if we except the minor local oscillations of land indicated 

 by the raised beaches on the islands of Bass Strait, and on other 



places along the northern coastline of Tasmania It may 



generally be affirmed that the leading features — the mountain 

 chains and ridges, the main valleys and their river coui'ses, 

 the great plains and plateaux — were all established prior to the 

 deposit of the members of the Post Tertiary age." The Henty 

 pene-plain, however, has been so deeply dissected that it is pro- 

 bably somewhat older than the glacial deposits, which in some 

 cases are comparatively fresh. 



The formation of the Henty pene-plain must have been a long 

 task, and must have been completed when Tasmania was less 

 elevated than it is now. It may have been contemporary with 

 the formation of the extensive dissected pene-plains, which are 

 among the most important features in the geography of Victoria. 



The date at which the pene-plain was uplifted is. though pre- 

 glacial, geologically recent. The most convincing evidence is 

 given by the narrowness of the river gorges that cut through it. 

 The railway between Emu Bay and Strahan runs for some 

 distance down the Pieman Valley, a deep and narrow gorge, the 

 bed of which is being rapidly deepened by corrosion. The Henty 

 River near Strahan flows across a low-lying alluvial plain, crossed 

 by lines of high, weathered, sand dunes ; but further to the east 

 this river cuts through the pene-plain in a very deep gorge. 



The best case, however, is that of the King River, which rises 

 in the central plateau of Tasmania. East of INIount Lyell it 

 flows through a broad, flat-floored valley, known as the " Long 

 Marsh." Here its valley is obviously of great age, but further 

 down its course the river flows through a sinuous, narrow canyon. 



Mr. W. T. Batchelor, the engineer of the Mount Lyell Mine, 

 kindly told me that in one place the depth is 1700 feet, where 

 the canyon is at the summit only between 2000 and 2500 feet 

 across. The narrowness of this river gorge, and the vertical 

 character of its clifl's, show that it is a very young valley. 



Further evidence indicating a comparatively recent uplift of 

 this part of Tasmania is supplied by the southern face of Mount 

 Sorell. This mountain is situated on the northern side of Mac- 

 quarie Harbour. It consists of a block of the West Coast Range 



