156 THE CANADIAN NATURALIST. [Vol. X. 



fri'quently portions of the original tests remain. In the region 

 under con>^ideration nearly 200 species of fossils have been 

 obtained from the beds of the Niagara group, yet the collector 

 may spend days and obtain a mere handful of specimens to re- 

 ward him for his trouble. 



It may be noticed here that there is a bed near the top of the 

 series at Dundas, several feet thick, that appears to be made up 

 of breccia, the fragments being derived from older portions of 

 the adjacent rocks. 



During the long period required for the deposition of the lime- 

 stones, the character of the organisms which inhabited the sea 

 was subject to some important changes. One of these conspicu- 

 ous periods has le^t its stamp in the " Chert beds," which are 

 classed as No. 12 of the sections. The average thickness of 

 this series of thin beds of limestone, filled with numerous 

 concretions of cherty material, is eighteen or nineteen feet. 

 The limestones are dolomites, as is shown by the previous an- 

 al3'sis. By far the greater proportion of concretions show no 

 organic structure, but yet, such large numbers when broken, show 

 the internal sections of sponges, which mostly belong to the 

 genera of AstijJospnngia and Aulocopiua^ that the origin of the 

 siliceous nodules is at once apparent. On some portions of the 

 brow of the escarpment, both at Hamilton and Dundas, these 

 beds form the summit, and as the surface soil of the rocks 

 weather, just beneath what is only a few inches of soil, the com- 

 plete forms of the sponges become exposed by the action of the 

 frost and of the plough. The sponge life was very considerable, 

 that it could have ajBForded a sufficient source for so much soluble 

 silica as to have produced the enormous amount of chert found 

 in these beds. We know also that the variety of species was 

 considerable. Nor was the sponge-life all that adorned the sea 

 at that time. These beds are by far the richest in variety of 

 species, from the lowest radiates to the higher types of life that 

 are found in the Niagara series. It is also worthy ol' notice that 

 it is in this small series that the greater portion of the rich 

 GrapfoUfe Jauvdj to be described in a succeeding paper, is found. 



Just beneath these beds (No. 11 and 10 j which are more 

 shaly in character (of which the upper strata are known as 

 ''blue building beds"), we find our greatest number of T^riV^o- 

 lites together with the high-type Crustacean, Pterogotas cana- 

 densis (Dawson), recently discovered by Col. Grrant. 



