80 AUSTKALASIAN ANTARCTIC EXPEDITION. 



other places, we find more dyke than we might reasonably expect. The field appearance 

 suggests that the dyke walls have been squeezed together by a pressure of varying 

 intensity at different points of the dyke plane. Where the pressure has been greatest 

 the dyke wall might have closed together, and where the pressure has been least the 

 dyke rock has formed a bulge. The normal width of a dyke is about 2ft., and the width 

 of the enlarged outcrops is 9ft. or 12ft. At the same time we find the dykes running 

 out of the thin parallel threads, and there are detached fragments of amphibolite adjacent 

 to the dyke channel or along its continuation, which are wholly surrounded by the 

 granodiorite gneiss. As far as observed, the foliation of the granodiorite gneiss bends 

 around the contour of these isolated fragments. Sometimes they are precisely similar 

 to the " canoe-shaped infolds " described in other areas. 



There seems to be no reasonable alternative but to consider these " inclusions " 

 as part of the dyke series. They have been shown to be so similar in character to the 

 normal dyke, and so dissimilar from the granodiorite gneiss. In metamorphic areas, 

 therefore, caution is necessary before we can assert the younger or the older age of the 

 enclosing rocks. With our interpretation the " inclusion " is the younger rock the 

 reverse of the normal igneous or sedimentary deduction. 



These abnormal dyke features demand an attempted explanation, especially as 

 we will subsequently infer that analogous cases may exist in other areas of metamorphic 

 rocks. One can, perhaps, imagine that branching offshoots of dyke into the adjacent 

 gneiss might become detached from the main dyke channel during a period of excessive 

 stress, and so form isolated fragments that lie adjacent and parallel to the main dykes. 

 Such, however, provides no mental picture of the manner in which the main dyke has 

 itself been rendered discontinuous. 



Possibly there is an analogy with some curious features in the Ordovician rocks 

 at Daylesford, Victoria, which have been recorded by T. S. Hart*. These Ordovician 

 sediments are a steeply folded series, and unequal thickening and thinning of slate 

 beds between sandstone beds is a common feature. The continuity of the slate 

 beds is often broken. In a railway cutting near Daylesford slate now appears in 

 numerous pockets of various shapes and sizes in a hard sandstone. At one place the 

 pockets possess a prominent linear trend which would correspond in position and 

 direction to a bed of slate. During the process of folding the slate has behaved towards 

 the sandstone as a relatively plastic rock. The slate bed has had a thickness comparable 

 in size with the minor irregularities and small displacements of the adjacent rigid 

 sandstone, and been squeezed out irregularly so that it is now represented by a number 

 of isolated fragments. The squeezing out of the slate goes so far sometimes as to show 

 only occasional slate patches along a definite line of junction of two beds. 



This, therefore, is the case of a primary band of solid rock that lost its identity 

 by the play of stresses which have resulted in nothing beyond folded sediments. Could 



* " On some Features of the Ordovician Rooks at Daylesford," T. S. Hart, Proc. Roy. Soc. Vic., vol. XIV., 



N.S. pt. II., p. 167. 



