[DAWSON] FOSSIL SPONGES AND OTHER ORGANIC KEMAINS 121 



remains of origans of fruotitioation or attache<l animal Htructures, or 

 merely inorganic ag^ro^ations, I have not been able to determine. 



Chndorites Metissicus, 8. n. 

 Flattened fronds, two to four millimetres broad and the largest eight 

 to ten centimetres long. They are riband-like and smooth, with even 

 edges and fork dichotomoiisly at angles of 40° or more. They show 

 traces of carbonaceous matter but no structure. 



In concluding this paper I think it proper to remark on the exuberance 

 of sponge life, both in abundance of individuals and of generic and specific 

 forms on a limited area of muddy sea-bottom of the lower Ordovician or 

 later Cambrian age, evidenced by the collections made at Little Metis, the 

 account of which in this paper is presented as merely the result of recre- 

 ative excursions in the summer vacation, in a tield different from that 

 in which the author is usually engaged. 



In a formation usually little productive of fossils, and in muddy 

 deposits, which must have been laid down in water at a low temperature 

 and ill the intervals of conditions producing beds of a coarse mechanical 

 character, this abundance of delicate organisms is very unexpected and 

 surprising. We have to observe also that if the sponges in question 

 were, like their modern allies, inhabitants of deep water, there must have 

 been considerable oscillations of level at the time when they lived, as well 

 as much deposition of earthy matters in circumstances unfavorable to 

 marine life, as evidenced in the great thicknesses of barren material inter- 

 vening between the sponge-bearing layers. 



Dr. Hinde has already mentioned the close alliance of many of these 

 Palu'ozoic sponges with their successors in later formations and in the 

 modern seas, evidencing the great permanence of the siliceous sponges 

 throughout geological time, and the fixation of the mechanical and vital 

 laws of their structure and growth at a very remote period. More 

 especially is this remarkable if we include with them the spicular forms 

 which have been recognized in the Laurentian, Huronian and Early 

 Cambrian rocks. The graptolites belonging to the oceanic waters of the 

 Cambrian and Ordovician have already indicated the paramount im- 

 portance of giving attention to the general oceanic fauna of these periods, 

 as well as to that of the continental plateaas, and it is possible that in 

 future the sponges may also prove of more value than heretofore in 

 regard to questions of relative geological age. 



The results of these observations at Little Metis, in connection with 

 the obscure and unobtrusive character of the fossils, also show how much 

 is in the power of local collectors, having time and opportunity to follow 

 up any discovery by excavation and continued collection. In this way 

 beds for the most part unfossiliferous and presenting few attractions to a 

 passing collector, may be made to yield unexpected scientific treasuree. 



MM 



