THE METAMORPHIC ROCKS OF ADELIE LAND -STILL WELL. 81 



the disruption of the amphibolite dyke channels at Cape Denison occur in a like 

 manner ? Can the primary dolerite dyke, under the more intense conditions which 

 have resulted in the decrystallisation, be considered a relatively plastic rock alongside 

 the granodiorite ? 



In this respect the only experimental data available are not encouraging. Adams 

 and Coker* have carried out an investigation into the elastic constants of rocks during 

 which they determined the cubic compressibility (D = ratio of the stress per unit area 

 to the cubical strain) of five marbles and limestones, six granites and four basic plutonic 

 rocks. The average of their results is 



D (in inch, pound units). 



Marbles and limestones 6,345,000 



Granites 4,399,000 



Basic intrusives 8,308,000 



These results show that the granites are much more compressible than the marbles 

 or the basic intrusives. The experimenters varied one set of readings over a 

 temperature range of about 30 C. and found no perceptible difference. The actual 

 case, however, under temperatures which are very high in comparison to living room 

 temperatures, may be possibly very different. 



These results are the reverse of what our proposed analogy would lead us to expect. 

 Yet we have the fact before us that the impressed conditions were sufficient to cause 

 the complete recrystallisation of the dolerite, but only a very imperfect recrystallisation 

 of the granodiorite. In this sense the basic rock has been more susceptible to the 

 superimposed conditions. 



With these experimental data we must picture the basic dyke as a sheet of hard 

 rock enclosed in a mass of relatively soft rock, viz., the granodiorite, and we must 

 endeavour to understand what would happen to the system under the influence of great 

 stress. If the hardness can be associated with brittleness, then, perhaps, we may picture 

 the fracturing of the brittle sheet and the production of isolated fragments. That such 

 fracturing actually occurs is shown by the observations of Adams and Barlow in the 

 Haliburton and Bancroft areas. These authors figure and describe the initial stages 

 in the disruption of an amphibolite dyke embedded in crystalline limestonef. The 

 basic rock, on the experimental evidence, is less compressible than the limestone, and 

 hence the experiments cannot furnish argumentative data against the disruption of a 

 basic dyke channel in granodiorite. 



We find further in the Kylesku to Loch Broom district, in the North-West Scottish 

 Highlands,^ that basic dykes have been observed to be wrenched into a series of isolated 



* " An Investigation into the Elastic Constants of Rocks," F. D. Adams & E. G. Coker. Pub. 46, Carnegie Inst. Wash., 

 June, 1906. 



f " Geology of the Haliburton and Bancroft Anas," F. D. Adams ft A. E. Barlow, Mem. 6, Can. Geol. Surv., 1910, fig. 

 G, p. 160. Plates XXIX., XXX. 



t " The Geological Structure of the North-West Highlands," Mem. Geol. Surv. Gt. Britain, 1907, p. 169. 



Series A, Vol. m., Part 1 F 



