18 GLACIAL REMAINS IN THE NATIONAL PARK, 



Mt. Mueller. We are, therefore, bound to conclude that the 

 diabase intrusion raised the country from Mueller to Styx 

 to an elevation of 4,000 feet, and similarly raised the Mt. 

 Field plateau, but left the valley of Tyenna-Westerway at 

 an altitude of less than 1,000 feet above sea level. 



From the Tyenna Valley, through which flows the Rus- 

 sell Falls (or Tyenna or Crooke) River, the edge of this: 

 diabase mass rises rapidly, attaining an altitude of 4,000 

 feet in a mile or so. The backbone of the range extends 

 roughly east and west from Mt. Mawson, through Mt. Mon- 

 ash, and Seager's Look-Out, to Mt. Field East, to which the 

 land rises steeply from the Tyenna Valley on the south. 

 From Mt. Field East and Mt. Mawson two large parallel 

 ranges stretch away slightly west of north, reaching to 

 the southern edge of the Derwent Valley, about 10 miles 

 farther north, and maintaining an elevation of over 3,000 

 feet. Between these runs the deep valley of the Broad 

 River. 



To the west of this system stands the third parallel 

 chain of the Tyenna Peak — Mt. Field West Range, a western 

 outlier from the main diabase mass, to which it is con- 

 nected by K. Col. The wonderful escarpment on the west 

 of this range, dropping nearly sheer to the Florentine Val- 

 ley, 3,000 feet below, represents the western edge of the 

 diabase upthrust in this part of Tasmania. 



These three great mountain ridges show the form of 

 the diabase intrusion. Sedimentary rock skirts the lower 

 slopes of the mountains from Mt. Field East to Mt. Mawson. 

 It then runs a mile or more up the valley of the Humboldt 

 Creek, and back round the end of Tyenna Peak, and right 

 across the western face of Mt. Field West. Undoubtedly, 

 the intrusive diabase took the form we now see it in, and 

 erosion has worn out the softer sedimentary rocks between 

 the lines of intrusion, forming the valleys now existing. If 

 any further proof were required that such was the case, and 

 not that water has worn the valleys out of a plateau of 

 solid diabase, we can find it in the Lake Hayes Valley, where 

 the face of the valley is lined with sandstone. 



Of course, erosion has affected the diabase mountain 

 tops to a certain extent, but the great valley regions of 

 the Park are caused by the absence of diabase there. The 

 columnar cliffs so common near the tops of all the mountain 

 ranges in this area probably represent the edges of laterally 

 intruded sills of diabase. 



