BIGSBY — PALAEOZOIC BASIN OF NEW YORK. 449 



4th. Further, he observes (L c. p. 480), " While the general di- 

 rection of the Appalachian chain is north-east and south-west, there 

 is a remarkable predominance of south-eastern dips throughout its 

 entire length. This is particularly the case along the south-east, or 

 most disturbed, side of the belt .... But as we proceed toward the 

 north-west, or from the region of greatest disturbance, the opposite 

 or north-west dips, which previously were of rare occurrence, and 

 always very steep, become progressively more numerous, and, as a 

 general rule, more gentle." From hence we deduce singleness of 

 action. 



5th. We find also (/. c. p. 507) that a gradually increasing in- 

 terval between the axes takes place as we advance north-westwards 

 from the south-east side, — another proof of the oneness of this move- 

 ment. 



6th. The geological features of the northern and southern extre- 

 mities of this great uplift are mainly the same ; that is, along and 

 around the axes of Vermont in the north, and Holston in the south. 

 Much stress is laid by Messrs. Rogers on the fact that, in the great 

 crust-rupture at Cincinnati, the Niagara group comes in direct con- 

 tact with the Hudson-River group (there very calcareous), the 

 Medina Sandstone and Clinton Rocks being absent from their proper 

 place. The movement itself probably belongs to the post-carboni- 

 ferous period ; or, anyhow, it is so moderate as, with other consider- 

 ations, only to create a break of stage. The absence (or dying out) 

 of the arenaceous Group E. at this place may be accounted for by 

 its position — in the centre of the Upper Silurian Sea. Cincinnati is 

 320 miles west from the centre of the Appalachian chain, and much 

 further from the eastern borders of the sea just alluded to. 



In places innumerable along the course of the middle and upper 

 Mississipi, considerably to the west of Cincinnati, the absence of 

 middle and upper Silurian and of many Devonian groups becomes 

 quite common, — and from simple exhaustion of force and materials, 

 as is generally supposed — not from plutonic disturbance. In this 

 direction we seem to reach the western limits of the central palaeozoic 

 basin ; for the prevailing rocks are arenaceous. 



I shall only speeify three instances of the deficiencies just men- 

 tioned. 



On the Mississipi, just above Grand Glaize Creek, and in Salt 

 Creek, near St. Genevieve, Trenton Limestone is only separated by a 

 little sandstone or shale from the Chemung group, — the Chemung 

 supporting Carboniferous Limestone (Shumard, Rep. on Missouri, 

 1855). Dr. Shumard reports a like fact in Lewis County. The 

 same rocks meet, and all the groups which usually intervene are 

 wanting. Professor Swallow, the State Geologist, testifies to the 

 same extensive deficiencies in the middle palaeozoic strata throughout 

 Missouri. 



It is to be remarked upon this, that at the distance of 800 to 1 000 

 miles from the great uplift traversing Vermont, New York, Penn- 

 sylvania, Ohio, &c, we may well suppose the existence of new con- 



