THE HAMILTON ASSOCIATION. 73 



I agree with Dr. Newberry, that, if the chert had been furnished 

 by hot springs, we must find it accumulated around the source of 

 supply — but we discover nothing of the kind. 



Admitting that diatoms are soluble and may be consolidated in 

 the manner described, I doubt very much if this explanation can 

 be deemed satisfactory. It fails to meet many objections that could 

 readily be made, I think. 



In a recent communication from a friend of mine in Chicago, 

 who has already named three new genera of Hamilton sponges (not 

 yet described) he mentions that he had obtained, in Tennessee, 

 recently, about twenty specimens of sponges very similar to the ones 

 discovered here from the same geological horizon, but fossilized in 

 an entirely different condition. It is probable the sea near the 

 " Laurentian Hills " contained more silica than the same water so 

 far south. 



The absence of Niagara chert was very noticeable in the 

 Island of Anticosti. Although I obtained a very large number of 

 fossils, there was not a sponge among them. 



I do not think either the " Clinton " or " Medina " rocks are 

 represented there (although a few fossils of the series may occur in 

 the limestones) These beds, perhaps, were confined to the inland 

 sea. The rocks at Anticosti were deposited under different con- 

 ditions, in an open sea. 



Note. — Since the above was written, I find from a paper 

 published by Sir Wm. Dawson, in the " Quarterly Journal of the 

 Geological Society," for Nov., 1888 (a copy of which he kindly sent 

 me) that he holds the same opinion as the late Mr. Billings, viz : 

 that the Clinton rocks are represented by limestones underlying the 

 Niagara beds in Anticosti. 



This view, perhaps, may have originated in the discovery of 

 similar fossils, which I failed to obtain. Fossils, however, are scarcely 

 safe guides there, — theyare so mixed up. For instance, — Graptolithus 

 Clintonensis, a characteristic Clinton Graptolite elsewhere, is found 

 well up in the Niagaras there, near the S. W. Point Lighthouse. 



