146 Notes on the Geology of Murray Bay. 



(14.) Similar limestone, Leperditia less numerous, also Stropho- 



mena and Modiolopsis 6 



(15.) Hard arenaceous limestone and calcareous sandstone, with 

 little vermicular cylinders in one bed, and fragments of 

 Pleurotomaria, &c., entire 20 



The above bed belongs to the lower part of division 3, of the pre- 

 vious general section, and above it there appears in the cliff 

 a considerable thickness of similar beds capped by the beds 

 of division 2, with some of the Trenton fossils enumerated in 

 the list attached to that division. 60 feet or more. 



When these Silurian rocks were deposited, the older Lauren- 

 tian series must have been much in its present state. It formed 

 a broken and indented coast lower than the present shore ; but 

 its beds were as hard and crystalline, and perhaps as much con- 

 torted as they now are. The sea beat against it as now, and this 

 for a very long time ; for the deposition of the Silurian sand- 

 stones was slow, as is evidenced by the thoroughly rounded 

 grains of sand of which many thick beds are composed, and 

 which indicate the toil of the waves for long ages on the Lauren- 

 tian shore, first, in breaking up its hard masses, then in grinding 

 these fragments and polishing them into perfectly rounded forms. 

 In the sandstones of some later formations, as for instance in the 

 carboniferous sy£'\em, the grains are usually angular, but in the 

 Lower Silurian, (and in conversation with Sir Wm. Logan, I find 

 that he has elsewhere observed this appearance,)time has been given 

 carefully to round and polish every grain. In modern times we 

 see such purely silicious and polished sands only on clean beaches, 

 where few remains of plants or animals are allowed by the waves 

 to remain, and perhaps this is connected with the absence of land 

 remains in these old beds. I had at first suspected from the forms 

 of these grains of quartz, that they might be concretionary like 

 those in some green-sand deposits, but microscopic examination 

 shows that they are not of this character, and discloses among 

 them occasional grains of felspar and other minerals in the same 

 rounded condition. 



The Silurian beds are not themselves undisturbed. They rise 

 sometimes with steep dips up the sides of the hills, and have been 

 thrown into anticlinal ridges. At one place near Little Mai Bay, 

 they run in a vertical position along the shore parallel to the older 

 series. ITere at high tide nothing is seen but the cliflf of Lauren- 

 tian rock, but at low tide a wide shore covered with boulders is 

 laid bare, and stretching along this are seen the edges of the ver- 



