336 GEOLOGY. 



of which it was perhaps the beginning. It has not been demonstrated 

 that the strata of this region were deformed at this time, and if they 

 were, the extent of the deformation has not been determined,. The 

 strata of the region were notably folded at a much later, time. 



In New Brunswick and Nova Scotia there is unconformity ^between 

 the Ordovician strata and those which overlie them, indicating an 

 emergence after the deposition of the Ordovician formations, and a 

 subsequent submergence before the deposition of the next younger 

 strata of the region. 



During the Ordovician period, as during part of the Cambrian, the 

 eastern interior sea seems to have been connected with the Atlantic in 

 the latitude of northern New England and the Gulf of St. Lawrence. 

 During the disturbances which closed this period, this connection 

 seems to have been closed. 



In the preceding paragraphs, the crustal movements referred to 

 have been mentioned as occurring at the close of the Ordovician. It 

 would perhaps be more accurate to say that their beginning marks the 

 beginning of the transition from the Ordovician period to the Ll Silurian. 

 The duration of the interval of transition was probably long. 



The separation of the Cambrian system from the Ordovician is 

 much less marked than the separation of the latter from the Silurian 

 which follows. For this reason it has been proposed to group the 

 Cambrian and the Ordovician periods together under the name Mopale- 

 ozoic, while the other periods of the Paleozoic are classed m^Neor 

 paleozoic. 1 J< r 



f JUrJ 



Economic Products. 



The formations of the Ordovician, especially those of the Trenton 

 stage, constitute one of the most productive horizons of oil and gas. The 

 Ohio 2 and eastern Indiana oil- and gas-wells have their principal source 

 in this formation. Both the oil and the gas are believed to be products 

 of the organic matter which was included in the rock at the time of its 

 deposition. 



The Galena and Trenton formations in Wisconsin and in the ad- 



1 Dana's Manual of Geology, 1895. » 



2 See Orton, 8th Ann. Rept. U. S. Geol. Surv.; Phinney, 11th Ann. Rept. ; also 

 the reports of the State Geol. Surv. of Ohio and Indiana. 



