56 PKOCEEDINGS OF THE NATIONAL MUSEUM vol. 76 



similarity, information regarding the geological history of their 

 several countries will proceed to grow more rapidly than it^has in 

 the past 50 years. 



Discussion of relative amoimts and rates of deposition of Ordo- 

 "vician foi^Tnations. — It has been suggested to me in recent years that 

 the great thicknesses attained by many of the Paleozoic formations 

 in the southern half of the Appalachian geosyncline indicate a more 

 rapid rate of deposition there than in other areas that received much 

 thinner sequences of deposits during the same geologic periods. 

 But I see no valid reasons for believing this. In my opinion the 

 difference in this respect between them is not so much in the rate 

 of deposition during times of submergence as in the relative fre- 

 quency and duration of such times. For instance, the 2,000-4,000 

 feet of calcareous shale and limestone that commonly make up the 

 Athens formation required a long time to lay down; and in my 

 estimation they were laid down no faster than were similar but 

 much thinner beds in the Mississippi and Ohio valleys. The proc- 

 ess of deposition in the latter was more often interrupted and, be- 

 tween the interruptions, of shorter duration; but during the times 

 when it was going on the average rate at which the sediments were 

 laid down was not much slower than in the case of the Athens. Of 

 and in these, doubtless, the average rate to the foot was much faster 

 than in most other places. But in those places where sandstones enter 

 to any considerable amount into the process of Athens deposition, as 

 to the east of Abingdon, Va., the thickness of the formation increases 

 correspondingly to as much as 10,000 feet or possibly much more. 



This general statement is made in full recognition of the rather 

 obvious fact that whatever the kind of marine deposit, be it mainly 

 or wholly of limestone or shale or sandstone, local conditions must 

 have affected and caused variations in the rate of deposition, 

 whether inference ascribes them to lack or uncommon availability 

 of clastic material or to relative deeps or to deposition in shallow 

 basins or troughs in which interruption of the process was likely 

 to occur frequently ; and at times the interruptions persisted through 

 long periods. Thus, only a few miles west of the thickest develop- 

 ment of the Blount formations in east Tennessee and southwestern 

 Virginia they pinch out completely, their place in the sequence of 

 formations being in a tight contact between Stones Kiver and Low- 

 ville limestones that remain in contact to the Mississippi River and 

 contain wholly distinct faunas of southern and not middle or north 

 Atlantic origin. Moreover, the Stones River wedges out eastwardly 

 beneath the Blount, and its lower formations interfinger in the 

 same direction with Lower and Middle Chazyan formations. The 

 Lowville, on the other hand, extends far eastward over the top of 



