THE DEVONIAN PERIOD 455 



Continent of Appalachia. — ■ The continent of Appalachia, situated 

 east of the present Appalachian Mountains, which during the pre- 

 ceding periods of the Paleozoic was supplying the streams with sedi- 

 ment for the Appalachian geosyncline, was extensive at this time 

 and was probably a broad, mountainous upland whose eastern bound- 

 ary may have been beyond the present eastern limit of the continen- 

 tal shelf. This conclusion is justified when the volume of sediments 

 laid down in the Appalachian trough is computed. Such a computation 

 shows that the crest of Appalachia would have had to be lowered from 

 five to seven miles to supply the Upper Devonian sediments, if it had 

 not extended beyond the continental shelf. (Barrell.) It seems likely, 

 therefore, that Appalachia extended from the edge of the Appalachian 

 trough eastward over the present site of the continental shelf and prob- 

 ably fifty miles beyond. The broad Appalachian continent probably 

 never reached Alpine heights, but was rather slowly raised as the 

 Appalachian trough sank. The sediments of the trough are those 

 formed from igneous rocks of the land which had been subjected to 

 chemical decay, and are not such as would have resulted from the 

 mechanical disintegration of frost or changes in temperature. The 

 sediments, moreover, are seldom coarse, showing that the streams did 

 not flow from a high, mountainous region in proximity to the sea. 



Igneous Rocks. — In Maine, New Brunswick, and Nova Scotia, 

 granite intrusions and volcanic extrusions took place during the 

 Devonian. The city of Montreal lies at the foot of a volcano, and there 

 are other volcanoes to the southeast. This was the first premonitory 

 indication of the movements which were later to form the great Appa- 

 lachian Mountains. When North America as a whole is considered, 

 the Devonian Period closed with almost no deformation. 



Devonian Oil and Gas. — A discussion of the Devonian would be 

 incomplete without mention of the important oil and gas-bearing 

 strata of West Virginia, Pennsylvania, and southwestern New York. 

 The oil and gas are more likely to be found at or near the crests of low 

 anticlines (p. 425) than in any other situation. 



Devonian of Other Continents. — Epicontinental seas were wide- 

 spread in Europe and Asia during the Devonian, and smaller seas 

 covered portions of Africa, South America, and Australia. The 

 Devonian of England is of unusual interest because of the develop- 

 ment of a continental deposit of red sandstone, called the " Old Red 

 Sandstone/' It appears to have been laid down under desert condi- 

 tions, although no gypsum or salt beds prove this contention. In 



