252 THE PENOKEE IRON-BEARINCi SERIES. 



here ao-areaate 870 feet in thickness. Tliat the (•llel•t^• hiyers of Wales and 

 Enghmd are ahnost wholly, if not wholly, of oro-anic origin seems to l)e 

 conclusively shown. Also, it is certain that a ))ai-t of the chert of Ireland, 

 Spitzbergen, and Axels island is of organic origin. Dr. Hinde concludes 

 that — 



It is true that the niiuiber of specimens of chert available for examination are 

 very few, and they might be regarded as insnflicient ol' themselves to warrant the 

 conclusion that this great thickness of rock, which at one locality on Axels island 

 reaches 870 feet, is du6 to the accumulation of the skeletal debris of siliceous 

 sponges; but taking into consideration the fact that beds of similar cherty rock, 

 which in Yorkshire have an estimated thickness of 1M» feet and in North Wales of 3,50 

 feet, can be pioved to be due to .sponge remains, there is nothing extravagant in the 

 supposition that this nuich greater thickness of rock has iiad a similar origin. 



These cherts in Great Britain are Carboniferous; those of Spitzbergen 

 and Axels island are Permian. It is of interest to note that these are the 

 terranes in which the most extensive beds of iron carbonate in Paleozoic 

 time are found. Further, the sponge remains ])ass into a "pure translucent 

 chert." If, as Dr. Iliude maintains, all this silica is derived from sponge 

 s))icules, it nnist wow in some cases be extensively i-earranged; for a large 

 part of the chert apjtears from the descriptions at the ])resent time tn be 

 chertv or chalcedonic silica in forms independent of organic remains. In 

 the Penokee cherts no evidence of organic origin for any of them has been 

 found. This fact does not seem, however, to Ix^ any proof that tlie chert 

 was not originally deposited in tlie form of sponge si)icules; for it the 

 silica in deposits so late as the Cretaceous has lieeii so extensively rear- 

 ranged as has the chert in the Trimmingham chalks, it would l)e strange if 

 similar deposits, so far back in geological time as the Penokee series, had 

 not lost the evidence of organic origin. 



Our conclusion is, then, that we have no .satisfactory proof as to 

 whether the chert of the Penokee series is an original chemical sediment or 

 the remains of life, liut the latter is considered more probable. Tlie (juan- 

 tity of chert which is contained, supposing the whole Iron-bearing belt to 

 be as rich in silica as are the upper horizons, could not have beeu lieyond 

 300 or 400 feet. It appears clear that original formations of chert have 

 occurred which have more than twice this thickness, so there is no improb- 



