MESOZOIC TIME — TRIASSIC AND JURASSIC. 745 



in the nearer mountains to the north, west, and south. These sources were 

 probably in the Highlands and other ridges of crystalline rocks ; the waters 

 and sediment certainly did not come from the Catskill Mountains to the 

 north, nor from the Alleghanies to the west. The outlet of the Hudson 

 Eiver of the period to the Atlantic is indicated, apparently, by the submerged 

 Hudson Kiver channel on the map on page 18. 



The barrier along the sea margin that kept out salt water and its living 

 species was evidently the remains of the old geanticline referred to on page 

 387. 



The coarse conglomerate at or near the top of the sandstone series, 

 observed at many points on the east margin of the Connecticut valley area, 

 and on the west or inner margin of that of Maryland, Virginia, and North 

 Carolina, in which many of the rounded stones are one to three feet in 

 diameter, and also the similar large stones, or groups of stones, occurring 

 isolated in some of the finer sandstones, are remarkable features of the forma- 

 tion. Rivers cannot transport so large bowlders, unless down rapid slopes. 

 The tide in an estuary opening seaward only moves quietly, and usually 

 makes muddy or sandy shores. Igneous eruptions are never attended by 

 ejections of rounded stones or bowlders. The stones, excepting those of 

 Triassic sandstone and trap, show by their kinds that they were from the 

 adjoining ridges or hills. Moving ice would carry them ; but the Blue Ridge 

 and other adjoining ridges at the present time are far from high enough to 

 have glaciers about their summits. The question arises : Were they high 

 enough then ? Was there, at or near the close of the period, an epoch 

 of unusual cold having icy winters and covering the adjoining ridges with 

 glaciers that carried bowlders, and made streams that bore floating ice laden 

 with stones out over the river or estuary waters ? 



o. Subsidence in progress during the deposition. — Since a thickness of 

 some thousands of feet was acquired in the several areas by the strata, and 

 the beds often bear evidence in their ripple-marks, mud-cracks, and foot- 

 prints of shallow-water origin, each of the troughs of valleys must have been 

 undergoing, during the slow accumulation, a concurrent subsidence of as 

 many thousands of feet. On the upturning of the beds and other orographic 

 phenomena see page 798. 



Economical products. — The coal-beds, already described, are a prominent part of 

 these products. Veins containing copper ores occur in Connecticut, New Jersey, Pennsyl- 

 vania, which have been worked ; but none are now producing ore. The copper ores are 

 chiefly chalcocite and bornite, with occasionally native copper. One mass of native copper 

 found in the drift north of New Haven, Conn., weighs nearly 200 pounds. A copper mine 

 at Bristol, Conn., which was for awhile productive, is situated on the western border of the 

 Triassic, in the crystalline rocks outside of the sandstone area, but belongs to a fissure of 

 the Triassic series. Barite often accompanies the ore, and sometimes is the chief mineral 

 of the vein, and occasionally occurs in crystals weighing over 100 pounds. A vein in 

 Cheshire, Conn., now exhausted, yielded a large amount of the mineral for the adulteration 

 of white lead, and for calsomining and other purposes. 



The beds of sandstone afford much rock for building purposes. The rock so used is 



