DISCUSSION. 



Professor James Hall: I .should like to express my great gratification 

 with the results of Mr. Walcott's iuvestigations. It leaves nothing, I helieve, 

 now to be desired beyond the bringing out of detailed results, which I dare 

 say he will do in the future. 



Professor W. M. Davis: This discussion gives me a desired opportunity 

 to explain a small matter, since I fear that a position I took several years 

 ago bearing on this question has been somewhat misunderstood. Some 

 time ago, when visiting the Hudson river valley with a class of students in 

 our Summer School of Geology, we examined the relations of the Hudson 

 River rocks and the overlying Helderbergs. The question of the relative 

 conformity of these two divisions had been much discussed, and we sought to see 

 how far the evidence there bore upon it. There are several sections, one 

 particularly on the Catskill stream not far from the town of Catskill, that 

 give fair opportunity for close examination of the lower and upper rocks. 

 My conclusion at that time was that, as far as that district was concerned, it 

 would be unsafe to say that there was a distinct unconformity between these 

 Hudson river rocks and the overlying Helderbergs. I did not wish to 

 assert that there was absolute conformity, but it seemed to me that with the 

 facts at Catskill alone it would be difficult to demonstrate unconformity; 

 that if there were at all other localities a perfect conformity, the observations 

 at Catskill need not disagree with that relation ; that the difference of alti- 

 tude of the lower and upper rocks about the Catskill was a discordance such 

 as might be produced by the folding together of the dissimilar rocks in that 

 region — the amount of discordance not being more than is often observed as 

 the result of folding masses of unequal resistance. But, on the other hand, 

 at Rondout, farther down the Hudson valley, it is manifest that there is a 

 strong unconformity, and I should not wish for a moment to use the obser- 

 vations at Catskill as proving a conformity at Uondout or anywhere else. 

 The point is that, as far as Catskill is concerned, the facts do not compel the 

 belief in the unconformity of the Helderbergs to the Hudson formation, and 

 that if no other locality of contact of these formations were known, their 

 relation might still be in doubt. 



Mr. Walcott: I have read Professor Davis's papers with interest and 

 profit, and I understood him to mean that the conformity between the two 

 series was only in the Catskill region, ami that there was an unconformity 

 at Becraft's Mountain, from the latesl paper published by him I obtained 

 tin- impression that he supposed a conformity to exist also at one of the sec- 

 tions in Rondout. I may have misinterpreted his description. 



(864) 



