112 Review of Recent Geological Literature. 
tensely altered condition and generally unique characteristics, as com- 
pared with those of any of the later groups ; and because of the lack of 
definite evidence of the existence of life during its production, while life 
plainly existed at the time of deposition of the earliest of the succeed- 
ing groups." 
The Huronian and Keweenawan, with perhaps other groups to be 
hereafter established, intervening between the Laurentian and Cam- 
brian, are classed together as Agnotozoic or Eparchaean, this term be- 
ing subject to future limitation or entire replacement, if any sufficient- 
ly distinctive paleontological discoveries shall be made. Professor 
Irving's classification draws the line between the Agnotozoic and Pal- 
eozoic systems at the base of the Potsdam, Saint Croix, or Lake Super- 
ior, sandstone in the succession of formations developed about lake 
Superior ; but he suggests that sufficient evidence may yet be found in 
Keweenawan and Huronian fossils for the extensioji of the Paleozoic 
system to include all these groups, excepting the basal Laurentian 
gneisses and schists. 
The structure of the Triassic formation of the Connecticut Valley. By 
William Morris Davis. Pages 455-490 ; plate lii (map of a portion of 
Connecticut) ; figures 97-108. (Accompanying the seventh report, TJ^ 
S. geological survey.) 
The present extent of this Triassic area measures about 95 miles 
north and south, from long Island sound, where it runs under the sea, 
nearly to the northern boundary of Massachusetts, and from 15 to 18 
miles east and west in central Connecticut and southern Massachusetts 
where it is broadest. The aqueous rocks of the formation consist of 
conglomerates, sandstones, and shales; they are mostly of a red or 
brown color but the shales are sometimes dark and bituminous, with 
impressions of fish and of land plants ; occasional thin seams of coal 
have been reported, and a small but significant bed of impure grayish 
limestone makes its appearance among the shales. 
• Interbedded with these sediments are dolerites or diabases, which 
occur as intrusive sheets along the western border of the southern 
half of the formation, and elsewhere and more commonlj' as overflows, 
lying upon the beds that had been formed at the time of their eruption 
and buried under the later deposits. 
A preliminary statement of the sequence and thickness of the Trias- 
sic series in the Connecticut valley, in natural order from top to bot- 
tom, is as follows : 
Thickness in Feet, 
Conglomerates, sandstones, and shales 2,000 to 3,000 
Posterior trap overflow 50 to 150 
Sandstones and shales 300 to 500 
Main trap overflow 300 to 500 
Shales with thin limestone 100 to 300 
Anterior trap overflow 50 to 150 
Shales 500 500 
Shales, sandstones and conglomerates 3,000 3,000 
Intrnsive trap sheet 200 to 400 
Sandstones and conglomerates 500 to 2,000 
Total 7,000 to 10,500 
