Bearing of Results on Time-Scale. 



I imagine that the transgressions which ushered in the great periods from 

 the Algonkian onward, were preceded by a deep-reaching disintegration of 

 the land. This vast amount of loose material was removed with ease and 

 rapidity by the breaching action of the advancing sea line. If we substitute 

 this process in each period for the accepted one of slow erosion and breach- 

 ing of hard rock, v/e shall, I think, have to materially reconsider our time- 

 scales in so far as they depend upon the rate of accumulation of detrital 

 materials. 



DISCUSSIOK 



Dr. George H. Williams: I had the pleasure, last summer, of visiting 

 most of the localities described by Professor Pumpelly, under his own guid- 

 ance; and I then, as now, w^elcomed his theory of secular disintegration as a 

 possible explanation of some of the difficulties encountered in my work on 

 the crystalline and semi-crystalline areas of Maryland. In my paper on the 

 Piedmont plateau in Maryland^ I have stated the evidence that these two 

 areas are separated by a time-break, which, however, does not seem to accord 

 Avith the transition observable between them. It seems as though Professor 

 Pumpelly's suggestion would go far toward removing this difficulty, if it be 

 taken in connection with the interchange of material which must take place 

 during the gradual metamorphism of rocks, thus obliterating any sharp line 

 of contact w^iich may have once existed between them. 



Professor B. K. Emerson: Professor Pumpelly's theory of secular disinte- 

 gration is applicable to the Triassic conglomerates of the Connecticut valley, 

 in this to some extent anticipating my paper on that subject.^ This paper 

 is based on precisely the same suggestion in reference to the beds of the Con- 

 necticut valley, in Massachusetts, where arkose deposits have been penetrated 

 3,000 feet by artesian well borings. The degree of rounding of the con- 

 glomeratic materials is in proportion to the absence of feldspars and the 

 sharpness of contact. Crossing Massachusetts, no Archean outcrop is met 

 w^ith until we reach the Douglas area, southeast of Worcester, where there 

 is an almost exact duplicate of the Hoosac mountain section, with basal con- 

 glomerate and quartzite surrounding a central mass of Archean rocks. 



Mr. G. K. Gilbert: I desire to call attention in this connection to a 

 process of conglomerate formation to which allusion is rarely made, but 



*riiuted elisewhere in this volume. 



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