1904.] HATCHER — MARINE AND XOX-MARIXE FORMATIONS. 363 



** are undoubtedly of shallow-water or near-shore origin and repre- 

 sent the ancient marginal deposits of the sea as it encroached upon 

 the land. Everywhere, next to the Paleozoic floor and conformable 

 to its slope, this bed of sand, which seldom reaches 200 feet in 

 thickness, persists as an apparent formation, blanketed between the 

 underlying Paleozoic floor and overlying calcareous beds, and 

 inclines toward the sea at a slightly greater angle than the latter. 



** While these Basement sands of the Cretaceous, both in the area 

 of outcrop and in that of the embed penetrated by the deepest wells, 

 have the aspects of a continuous formation, they are in fact the 

 interior margin of many formations, and were in process of deposi- 

 tion during a long period of time, and their successive layers are of 

 later and later age as one descends the slope of the old Paleozoic 

 floor." 



The whole discussion from which these sentences are quoted is a 

 clear description of an apparently continuous deposit which is not 

 of the same age in different parts of its area, and which is thus an 

 illustration of the principle that Hatcher especially emphasized. 

 Such conditions are exceptional, however, and it by no means 

 follows, as Hatcher seems to have supposed, that all, or even most, 

 littoral and non-marine formations were extended only by accre- 

 tions along their borders, and consequently that if they cover any 

 considerable area the time required for their deposition is propor- 

 tionally long, or, to quote Hatcher's words, that the time interval 

 ^' should be estimated not so much by their vertical thickness as by 

 the extent of their geographical distribution." In cases like those 

 above cited it is usually possible to determine the true character of 

 the deposits and to form, some idea of the time interval represented 

 by them by studying the associated formations. If a conformably 

 overlying formation is the same throughout the area occupied and 

 shows no change in paleontologic contents, we must conclude that 

 the interval represented by the upper layers of the deposit in ques- 

 tion is brief in a geological sense, although we may be convinced 

 that the deposits at different localities were not strictly contempor- 

 aneous when measured by the smaller time units of human history. 

 The fact that in certain cases a formation may not be strictly con- 

 temporaneous throughout its geographic extent is not denied, but 

 the relative importance of this fact in its bearing on paleontologic 

 and stratigraphic work is questioned. In my opinion it is greatly 

 exaggerated in the third ot Hatcher's conclusions. 



