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tombed in the rock, and endeavours to arrive at some general 

 conclusions regarding the condition of things in the past, by a 

 comparison of these remains with others of animals now existing, 

 and of whose life history we have the means of learning something 

 definite. In the present case this kind of evidence fails us entirely, 

 and we are compelled to fall back upon the evidence aiforded by 

 the physical character of the rock for the elucidation of this point. 

 Fortunately the Penrith Sandstone presents many features that are 

 full of significance to the geologist, and we may, I think, venture 

 to base our reasoning upon these almost as safely as upon any 

 evidence derived from a study of the fossils, although it may be 

 necessary to follow up this evidence in a round-about kind of way. 

 I have pointed out that the rock we are now on is the result of 

 successive accumulations of sand in the bed of an old lake. The 

 deposition of such a mass of sediment (which, in the Eden Valley 

 alone, is probably not far short of fifty cubic miles even in the 

 present fragmentary remnant of the rock,) implies that an equal 

 quantity of material has been slowly reduced to a transportable 

 form from a pre-existing mass of rock somewhere else, and after- 

 wards transferred to this its present resting place. It is important 

 to discover where that mass of rock lay. The Penrith Sandstone 

 hereabouts largely consists of grains of quartz, mingled with a 

 smaller quantity of bits of kaolinized felspar. Mica, the mineral 

 that usually accompanies these two in almost every sedimentary 

 rock where they are present, is absent almost entirely in this rock. 

 Now there is this peculiarity about much of the quartz, as Pro- 

 fessor Harkness was the first to point out, that whereas in ordinary 

 sandstones it usually occurs in the form of little rounded grains 

 without any general uniformity of outline, in the Penrith Sandstone 

 it occurs in the form of double six-faced pyramids, occasionally 

 slightly worn, it is true, but still recognisable by the thousand. It 

 is these that impart the rough grain and the sparkling aspect to so 

 much of the stone used for building about Penrith. Similar 

 double pyramids occur commonly enough in many rocks of 

 plutonic origin, and crystals of the same form may be developed 

 in a rock in other ways. But some of these doubly-terminated 



