208 STRATIGRAPHICAL GEOLOGY. 



Conclusions. 



Four important conclusions may be drawn from the distribution of the 

 formations in north-western Maine, when compared with the rock-expos- 

 ures in New Hampshire and elsewhere. 



1. The Oriskany sandstone reposes gently upon Eozoic gneisses, the 

 first bearing scarcely more traces of alteration than the corresponding 

 group in New York, while the second seems to have been metamor- 

 phosed and elevated before the Devonian formation was deposited. No 

 further trace of this group has yet been found towards the White Moun- 

 tains. It has been followed through Maine from one hundred and fifty 

 to two hundred miles, and similar rocks are described in Nova Scotia by 

 Dawson. It can, therefore, no longer be maintained with reason that 

 these strata pass into New Hampshire in a metamorphosed condition. 

 Furthermore, since the Oriskany and Helderberg formations are so dis- 

 tinctly f ossiferous in immediate juxtaposition with the crystalline strata, 

 it affords a presumption that the latter groups have not been altered 

 from any other Paleozoic sediments. 



2. The Oriskany is several times thicker than its extension in the 

 interior and farther south in Pennsylvania. The greatest thickness men- 

 tioned by H. D. Rogers is five hundred and twenty feet, about one fifth 

 its dimensions in Maine. The greatest observed thickness in New York 

 is only thirty feet. 



3. The discovery of nev/ localities of Helderberg limestone indicates 

 a wide-spread submergence of eastern America, in Upper Silurian and 

 Middle Devonian times, of nearly fifteen hundred feet. These fossils 

 have been detected at Bernardston, Mass., Lyman and Littleton, N. H., 

 perhaps Orleans county, Vt., Montreal, Lake Memphremagog, and other 

 localities to the north-east in Quebec province, Eustis, Flagstaff, and 

 Spencer mountain, in the field described above in Maine, and still greater 

 developments in the northern part of Maine, too extensive to be specially 

 mentioned ; — hence, 



4. There must have been, subsequently to the Helderberg, a period of 

 elevation to bring New England to essentially its present condition. Pos- 

 sibly this epoch may be indicated in the later elevating force seen upon 



