3O CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [Bull. 



(in connection with the assumption, regarded as compulsory, of 

 permanent water bodies coextensive with the sediments) to the 

 hypothesis that the Connecticut Valley in the Triassic was a 

 tidal estuary, in which the ebbing tides permitted the develop- 

 ment of the marks of subaerial exposure. But the presence of 

 these marks in most parts of the formation, and not exclusively 

 near the margins of the area, shows rather that the water bodies 

 were migrating rivers or shifting lakes, and that the sediments of 

 river flood plains of great breadth were subjected to periodical 

 drying. The Triassic sediments are therefore best regarded as 

 mainly river deposits of an inland basin, and, if the sea ever 

 gained access during this period, the evidence of it has not as yet 

 been developed. 



In these sediments feldspar and mica (muscovite) are abun- 

 dant constituents, washed in as undecomposed minerals from the 

 hills of crystalline rocks. But the black minerals in these rocks 

 owe their color to iron and part of this is only in a partially 

 oxidized (ferrous) condition. These iron minerals, chiefly horn- 

 blende and black mica (biotite), as well as all organic matter, 

 were, in this Triassic climate, with rare exceptions, oxidized and 

 destroyed, the iron oxide (ferric oxide) thus set free giving rise 

 to the dominant red color of the whole formation. Such condi- 

 tions of partial chemical decay of granitic minerals are found in 

 the basin deposits of semiarid climates, such as those of parts of 

 Spain, New Mexico, and southern California; and it is to such 

 regions that we must turn to find the nearest existing analogues 

 to the climate of Connecticut in the Triassic period. 



The marginal conglomerates contain some rounded cobbles of 

 granite and quartzite, showing that they have been rolled by rivers 

 at least some miles. They are rarely, however, more than six or 

 eight inches in diameter and more commonly average two to four 

 inches, though in a few places diameters of one or two feet are 

 found. The rivers therefore were stream's of moderate current, 

 not rushing into the basin as mountain torrents. Along with the 

 rolled cobbles and the mud and sand are mixed, however, angular 

 fragments of soft schists and glistening crystals of feldspar, 

 which show by their unworn nature that they have suffered but 

 little transportation and testify to the existence of gravelly wash 

 from near-by hills covered with but scanty vegetation. 



