524 Prof. E. Hull— Origin of Chert 



distinct as they are if these steep mountain-sides had been exposed 

 to annual rainfall of 100 inches for the last 200,000 years? 



Above Grasmere there is a small lake, know as Easdale Tarn, 

 which seems to have been partly formed by a terminal moraine, 

 while earlier ice-markings down the valley seem to indicate that the 

 glacier formerly pursued the same course which the stream from the 

 tarn now follows. Though the drought of the season had been 

 remarkable this stream was not a very small one, yet the work of 

 erosion done by it since the Glacial period was not of a very startling 

 description. It was not what I should expect a rapid mountain- 

 stream (though checked by a small tarn) to effect in 200,000 years. 



Such phenomena are by no means peculiar to the Lake District. 

 The great fall of Niagara seems to be an example. There is, I 

 believe, no trace of an earlier post-glacial river-channel. On the 

 contrary, the ice-markings almost down to the water's-edge above 

 the fall seem to show that the glacier followed the same track as 

 the river. The river must, therefore, have commenced cutting out 

 of the gorge as soon as the ice-cap cleared away. But Sir Charles 

 Lyell estimated the time necessary to cut out this gorge at 35,000 

 years, while others have placed it as low as 12,000. Professor 

 Winchell has estimated the time required to cut out the gorge below 

 the falls of St. Anthony at 8000 to 10,000 years. I am not aware 

 that there is any reason to think that this excavation did not com- 

 mence until long after the close of the Ice Age. 



Man probably existed on the earth in the Glacial, if not the 

 Pre-Glacial, era. But is there any reason to suppose that he existed 

 for at least 200,000 years without making any solid progress in 

 civilization, and then suddenly made the great advances (emanating 

 apparently from more than one centre) which has taken place in the 

 last 10,000 (or perhaps 6000) years? It is not a case of an 

 anthropoid ape slowly developing into a man during a period of 

 200,000 or 800,000 years ; for the earlier skeletons appear to be 

 those of fully-formed men. 



For these reasons I think Dr. Croll refers the Ice Age to too 

 remote a period. Further researches on the amount of post-glacial 

 erosion and the erosive power of the streams or rivers engaged in 

 it ought, I think, to enable us to decide the question one way or the 

 other with a tolerable degree of certainty. 

 Dublin, Sept. oth, 1887. W. H. S. MoNCK. 



DR. HINDE ON THE OEIGIN OF CAEBONIFEEOUS CHERT. 

 Sir, — Permit me to reply to the article by Dr. Hinde, F.G.S., 

 which appears in the Geological Magazine for the present month 

 (No. 280, p. 435). As I had an opportunity when attending the 

 meeting of the British Association in Manchester of hearing the 

 paper read in Section C, and as I had previously had the pleasure of 

 a visit from its author in this city, I was not unprepared for the 

 onslaught which afterwards took place. I have no wish to maintain 

 a position which subsequent investigation has shown to be untenable, 

 or which requires readjustment; and I am, therefore, quite ready 



