34 DAWSON AND HINDB 



The Ibllowiug is a more detailed section of part of the second division above, in 

 descending order, measured on the surface of the outcroji : — 



INCH. INCH. 



Black shale 8 Black and gra)' shales, with remains of sponges 



Dolomitic band (weathering yellow) 3.1 in some layers 72 



Gray and black shales , 12 Dolomitic band 2 



Dolomitic band 1 Black and gray shales 34 



Black shale 6 Dolomitic band 3 



Gray and black shales 15 Black and gray shales 3G 



Black shale 8 Black and gray shales (sponges, &c.) 



Gray and black shales 30 Black and gray shales,with thin, interrupted dolo- 



Black shale (sponges, &c.) 3 mitic layers as before, to base of the division. 



A third sponge-layer was found in the lower beds, about 30 feet vertically, or 50 

 feet measured on the shore, below the last dolomitic baud. The sponges contained in 

 the layers mentioned above, are apparently confined to a small thickness of the shale, 

 but in this are quite abundant. They are perfectly flattened, and their spicules are 

 replaced by pyrite ; but in some cases they retain the outline of their form, and have their 

 root spicviles attached. The spicules were, no doubt, originally siliceous, but they have 

 shared the chemical change experienced by other fossils in this bed, whereby they have 

 lost their siliceous matter and have had pyrite deposited in its place. In some cases, also, 

 the pyritised spicules have been frosted with minute crystals of the same substance, 

 greatly enlarging their size and gi^àng them a mossy appearance. This pyritisation of 

 spicules, once probably siliceous, is not uncommon in Palœozoic rocks, and it arises from 

 the soluble condition of the silica in sponges, and its association with organic matter, 

 which, in some modern sponges,- as in Hyalonema, enters into the composition of the 

 spicule itself. These spicules, therefore, suffer the same change with the calcareous 

 shells associated with them. 



Many of the sponges in these beds were entire when entombed. Others are decayed 

 and partially broken up, and there are some surfaces covered with confused patches of 

 loose spicules arising from the disintegration of many specimens. 



Some remarks are perhaps necessary here respecting the appearance of sponges in 

 different states of preservation. Of course the original textures of sponges are different, 

 and those which have consolidated spicules or firm external cortex, are those most likely 

 to retain their original forms. Even the looser kinds of sponges, however, may under 

 certain circumstances, preserve their rotundity of form. In this case they usually show 

 external markings, but not so well internal structure, unless when sliced. On the other 

 hand when completely flattened, which is usually the case in shaly beds, only an out- 

 line of the general shape remains, and sometimes not even this, while the forms and in 

 part the arrangement of the spicules are usually apparent. Farther, the hollow and 

 thin-walled species are more liable to be completely flattened, though in some cases, as 

 in the Devonian Dictyospongise, they may retain their form. It was this property, and 

 the membranous appearance of the outer coat, that for a long time sustained the belief ■ 

 that these last were plants rather than sponges. 



In the case of the sponges procured in the shales at Little Metis, perfect flattening 

 has occurred, and in many cases the spicules have been separated, and appear as mere 



