46 J. D. Dana on the origin of some of the 



is necessary in order to an appreciation of tlie observations that 

 folloAV. 



2. General course op Geological events before the Post-tertiary era. 



One of the last events of the Paleozoic ages was the formation of 

 the Connecticut River valley, by the bending of tlie earth's crust ; 

 and this took place as a sequel to, or in connection with, the crystalli- 

 zation of the granite, gneiss, crystalline schists, and other similar rocks, 

 which make the bottom of the valley. 



The first fact of the succeeding age, the Reptilian, of which there is 

 record, is the existence of a Connecticut valley estuary, twenty miles 

 or more wide, stretching from New Haven to northern Massachusetts, 

 (New Haven being the proper southern termination of the valley and 

 estuary), and the commencing deposition in this estuary of the Red 

 Sandstone formation. The production of this formation is believed to 

 have taken the whole of the Triassic period, the first period of the 

 Reptilian age, and also part of the next or Jurassic period. 



After, if not before, the close of the Sandstone era there were erup- 

 tions of trap — a rock that came up melted through wide fissures in the 

 sandstone and subjacent rocks. East and West Rock, Pine Rock, 

 Mill Rock, Mt. Carmel, tlie Meriden Hills, are ridges of trap along 

 with what remains of the old sandstone walls. Tlie sandstone in the 

 vicinity of the dikes, or near any fissures, tlirough which heat and 

 vapor escaped, was more or less hardened by the heat, and rendered 

 comparatively durable ; while other portions were left unhardened 

 or but little so, and therefore in a state admitting of easy erosion and 

 removal. Cotemporaneously with the ejections of trap, veins of cop- 

 per were made, as those of Bristol, Simsbury, Cheshire, etc. ; and 

 veins of barytes, as those of Cheshire. 



The thickness of the sandstone formation in the New Haven region 

 is not yet ascertained ; in Massachusetts, it is according to the lowest 

 estimate three or four thousand feet. There is abundant evidence 

 that its beds once covered the top of East Rock, now 360 feet in alti- 

 tude, and if so it reached upward to a level which is now at least 400 

 feet above the sea. Many of the trap ridges to the north in the 

 Connecticut valley were also once topped with sandstone, although 

 much higher than East Rock. West Rock has a height of 400 feet, 

 and the West Rock ridge, between Hamden and Woodbridge, over 

 500 feet; Mount Carmel about 800 feet; Middletown mountain is 

 899 feet high ; West Peak, the western summit of the Meriden Hang- 

 ing Hills, 995 feet; Mount Holyoke 985 feet, biit the highest point of 

 the Holyoke ridge, a little farther to the east, 1126 feet; and Mount 



