TRIASSIC PERIOD. 423 



accounted for by supposing that the dry land stretched farther to the 

 eastward than now, and that seashore deposits were formed which aro 

 submerged. A change of level of five hundred feet would take a 

 breadth of eighty miles from the ocean, and add it to the continent. 



This important fact — which has been before referred to, more than 

 once, on account of its bearing on the history of the continent — is 

 presented to the eye in the accompanying map, prepared from one of 

 the charts of the Coast Survey. The dotted lines (lines of equal 

 soundings) run back in a long loop northwestward, toward New York 

 harbor, showing deeper water along this line, and evidently proving 

 that once the land was above water, with the Hudson River occupying 

 this channel on its way to the ocean. At two or three places along 

 this channel, there are " deep holes," as they are called (one of them 

 at 32, where the depth is thirty-two fathoms), which may have been 

 former sites of New York harbor ; for the waters of the harbor are 

 now about six fathoms deeper than those about its entrance. An 

 under-water channel of the Connecticut also is indicated at c, c', c". 



This border, now submerged, has, therefore, in former time, been 

 dry land ; it may have been partly so in the Triassic period, and thus 

 have caused the imperfect connection of the Triassic areas of the 

 Atlantic Border with the ocean. 



The Triassic continent spread westward to Kansas, and southward 

 to Alabama; for, through this great area, there are no rocks more 

 recent than the Paleozoic. 



While, on the east, the continent probably stood above its present 

 level, through the Triassic period, and while, over much of the Rocky 

 Mountain region, the land was barely emerging from the waters, or 

 was covered by interior salt seas, — farther west, over a large part of 

 the Great Plateau, and the rest of the Pacific slope, the surface was 

 washed by the waves of the Pacific, and peopled with its life. The 

 Sierra Nevada was then no barrier to the ocean ; for the sands, mud, 

 and limestone accumulated in those waters constitute some of its 

 rocks. The stratified beds of the mountains were then in progress of 

 formation, through the action of the Pacific tides, currents, and waves, 

 and the growth of marine life. The making of the Sierra was de- 

 layed till the rocks of still another geological period had been deposited 

 upon the Triassic. 



2. Foreign Triassic. 



The region over which Triassic rocks outcrop, in England (see map 

 on p. 344), stretches across the island, from a point in its southwestern 

 part on the British Channel, north-northeastward ; and also, from the 

 centre of this band, along a northwestward course, to Liverpool, and 



