276 REPORTS OP COMMITTEES. 



a general W.N.W. dip. The matrix is seen under the microscope to 

 be made up of comminuted fragments of the Ordovician shales and 

 quartzites. 



The boulders in the gritty hard boulder clay are mostly rounded 

 or subangular ; occasional angular fragments may be seen of black 

 jasperoid slate, and quartz or quartzite. The boulders are mostly 

 from lin. to 2in. up to about 8in. in length. More rarely large blocks 

 up to 5ft. in diameter are met with, the latter being mostly well worn. 

 Here and there are lumps or masses in the boulder clay, resembling at 

 first sight large erratics ; these are of rounded or irregularly oval shape, 

 and often exhibit a slight concentric structure. They merge insen- 

 sibly in some cases into the boulder clay of the base at their margins. 

 The diameter of these masses varies from 1ft. to 27ft. 



In the one shown in the photograph [exhibited] the thin beds of 

 conglomerate, locally developed in the till, are nearly vertical as regards 

 their bedding planes where they abut against the block. The block 

 itself is formed of very fine sandstone, showing extremely minute 

 diagonal bedding. It would seem from the shape of some of these 

 fine-grained masses of hard fine-grained sandstone that they were 

 bent out of shape slightly subsequent to the time of their deposi- 

 tion. 



As regards the shape of the typical boulders, they are either flat- 

 tened oval, or somewhat blunt-pointed at one end, and more squared 

 o£E at the other end, like a short boot. Frequently one of the two 

 larger surfaces is flat, while the other is more convex. In such cases 

 the flat side is usually uppermost when the block is in situ in the boulder 

 clay. For the most part the lie of the longest axes of the boulders is 

 irregular, as is also that of their principal planes, which are inclined 

 at all angles with regard to the horizon at the time of their deposition, 

 being frequently vertical. Some of the included fragments in the 

 boulder clay appear to be true water-worn pebbles derived from older 

 rocks and subsequently glaciated. 



As regards glacial markings, a large proportion of the boulders 

 are intensely glaciated, being deeply grooved and strongly striated. 

 In many cases faulting may be observed, as might be expected. The 

 hardest rocks, such as the quartzites, quartz, and jaspers, have resisted 

 the glaciating forces. 



As regards the nature of the rock in these blocks, some of the most 

 angular, from Sin. to Gin. in diameter, are blackish jasperoid or cherty 

 argillite, passing into a black slate. The latter contain numerous 

 impressions of Graptolites {a). 



A common rock, occurring in blocks from Gin. to about 15in. in 

 diameter, is an ocLerous brown soft sandstone, with numerous hollow 



(o) There can be little doubt that the rock pavement underlying the boulder 

 beds in the vicinity is formed chiefly of these blackish graptolite rocks of the 

 Ordovician series. Mr. T. S. Hall, M.A., Lecturer in Biology, University of 

 Melbourne, the well-known authority on Australian Graptolites, has identified 

 Phyllograptits and Diplograptus among these specimens, as well as examples of 

 the Phyllocaridffi and shells of Brachiopods allied to Obolella. 



