2O CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [Bull. 



its close, were so great in the Connecticut area as to transform 

 them completely into crystalline schists and gneisses. All fossils 

 which they once may have contained have been obliterated, and 

 the age of the sediments, further than that they belong to the 

 Paleozoic, is not positively known. 



The third group of formations comprises the intrusive igne- 

 ous rocks of Paleozoic age. They are mostly granite-gneisses, 

 forced at repeated intervals into the older rocks as molten masses 

 of great volume, solidifying into granites, later crushed into 

 banded rocks known as gneisses. Their invasions record times of 

 revolution, of uplift and mountain-making, even as the sediments 

 into which they were forced record times of quiet and local sub- 

 sidence. The intrusive rocks probably belong mostly to the clos- 

 ing periods of the Paleozoic, when the ancient order of lands 

 and seas and the life inhabiting them was being broken up, and 

 the world stage was being reset for the drama of the Age of 

 Reptiles. But, since the sediments are not precisely dated, 

 neither can the age of the granite-gneisses be definitely known. 

 Farther west, in New York State, seas prevailed much of the time 

 until near the close of the Paleozoic, and the unmetamorphosed 

 strata record with fulness the progress of life and the sequence of 

 the ages. But near the western border of New England -many 

 formations disappear, others change their sedimentary character, 

 metamorphism masks their original nature, and before the Central 

 Lowland is reached they pass into a tangle of metamorphic and 

 igneous rocks, a second Basement Complex, only less profoundly 

 changed than the pre-Paleozoic Complex below. Indeed, until 

 within recent years no separation was made between them, and 

 the greater part of Connecticut, with the rest of New England, 

 was regarded as made of rocks of Archean age. Although 

 the original nature of the sediments is so greatly blurred, the 

 metamorphism and igneous intrusion clearly record a history still 

 more impressive to the imagination; for they are the basement 

 structures of an ancient range of mountains, the Paleozoic Alps 

 of New England, a generation of mountains long since vanished, 

 but whose rugged slopes and majestic heights the mind of man 

 has learned to build anew. 



The fourth group of rocks shown on the structure sections 

 is that of the Triassic sediments and lavas. The sediments are 



