420 MESOZOIC TIME. 



necticut and New Jersey, contain copper-ore (copper-glance, erubescite 

 and malachite) ; and there is little doubt that the copper veins and the 

 barite (sulphate of barium), which is often the gangue of the vein, 

 originated in the same period of eruption. The red color of the 

 sandstone — a consequence of the oxydation of iron present in it — 

 appears to have had its origin in the same cause. 



This history of the Triassic of the Atlantic border and its trap 

 dikes appears to be a repetition of what took place long before, during 

 both the Huronian and the Lower Silurian eras, in the Lake Superior 

 region, where a similar subsidence (at least 10,000 feet in the former, 

 and 3,000 or 4,000 in the latter) and similar igneous eruptions accom- 

 panied the formation of the beds. 



IV. General Observations. 



General Progress. — The following points bear upon the history of 

 this period in Eastern North America : — 



I. The position of the rocks in linear ranges, parallel with the moun- 

 tains, and therefore along depressions in the surface that existed when 

 the period opened. — The Connecticut valley is one of the great depres- 

 sions. Such areas would naturally have become inlets of the sea, or 

 estuaries, river-courses, lakes, or marshes, and would have received the 

 debris of the hills brought in by streams. 



II. TJie absence of Radiates, the paucity of Mollushs, and the presence 

 of few species that are properly marine. — These facts prove that the 

 ocean had imperfect access, where any, to the regions ; that the beds 

 were therefore estuary or lacustrine, and not sea-shore formations like 

 the Cretaceous and Tertiary of later times. The occurrence of vege- 

 table remains and of the coal beds sustains this conclusion. 



III. The mud-cracks, raindrop-impressions and footprints. — These 

 show, wherever they occur, that the layer was for the time a half- 

 emerged mud-flat or sand-flat ; and, as they extend through much of 

 the rock, there is evidence that the layers in general were not formed 

 in deep water. They abound especially in the upper half of the Con- 

 necticut-valley strata. 



IV. The occurrence, in some parts of the Connecticut valley, of 

 coarse conglomerate, some of the stones of which are very large, and 

 of a coarse kind of oblique lamination in much of the rock, is evi- 

 dence that some of the beds were deposited by a flood of waters pour- 

 ing violently down this valley ; and they seem also to indicate that 

 floating ice must have been concerned in part of the deposition. The 

 granitic and unassorted character of the sands looks as if the material 

 had been made by the disintegration of New England rocks, through a 



