132 Prof. J. D. Dana on some Results of 



also the local disturbances in the Primordial of Newfoundland, 

 as well as the facts relating to minor changes of level. 



a. Mountain- making on the Atlantic border. 



1. At the close of the Lower Silurian, or a little earlier, a 

 culmination of the great Appalachian geosynclinal resulted in 

 displacements, plications, and metamorphism, and the making 

 of a synclinorium along the Green- Mountain region, these 

 mountains (some summits at present over 4000 feet high 

 above the sea) being the result. The depth to which the region 

 subsided during the Lower Silurian era, and the thickness of 

 the accumulations, are not ascertained ; probably the extent was 

 not less than 20,000 feet. 



2. Simultaneously a permanent anticlinorium was made over 

 the Cincinnati region, from Lake Erie into Tennessee, parallel 

 to the Alleghanies of Virginia, 250 miles to the north-west. 



3. The Acadian region (embracing western Newfoundland, 

 St. -Lawrence Bay, the Bay of Fundy, and part of Nova Scotia 

 and New Brunswick adjoining, and probably the sea south-west 

 between St. George's Bank and the coast of Maine, with also an 

 area in Bhode Island) was the course of a great geosynclinal, 

 or a series of them, parallel in general direction to that of 

 the Appalachian region; it continued in progress^ but with 

 mountain-making interruptions and some shift of position to 

 the eastward, from the Silurian to the close of the Jurassic. 



At the close of the Lower Silurian no general disturbances 

 occurred in this Acadian region, so far as is known. In the 

 Anticosti seas, or northern part of St. Lawrence Bay, limestones, 

 as Logan states, were uninterruptedly in formation from the 

 beginning of the Hudson period of the Lower Silurian to the 

 middle of the Upper Silurian, showing that the Acadian geo- 

 synclinal was then in regular progress. It so continued until 

 the close of the Devonian, when disturbances, plication, and 

 metamorphism took place in eastern Canada, Nova Scotia, and 

 the bordering region of New Brunswick, and the most exten- 

 sive of Acadian Palaeozoic synclinoria resulted, according to 

 the observations of Dr. Dawson and others. 



4. The close of the Carboniferous age was an epoch of moun- 

 tain-making in the Alleghany region — the Alleghanies from 

 New York to Alabama having been then made, as already 

 explained. 



5. At the same time there were disturbances and synclinorian 

 plications in the Acadian region. During the Carboniferous 

 era, according to Logan and Dawson, 16,000 feet of rock had 

 in some parts accumulated; and therefore a geosynclinal of 

 16,000 feet formed — the rocks in their many coal-beds and root- 



