. Annual Reports of the Department of the Interior for the Fiscal Year Ended June 30, 1900--Twenty-First Annual Report of the United States Geological Society. ving been individuallyseparated into segments by parting planes perpendicular to their mainaxes (.see PI. 111). In the small neck shaped hill one-fourth of amile northwest of Pompt^raug Valley Station the upper surface of theexposure is crossed by thin silica veins to form a honeycomb-likenetwork, suggesting that prismatic jointing cracks have here Ijcensubsequently healed by infiltration of silica. It is not uncommon to find numerous m
. Annual Reports of the Department of the Interior for the Fiscal Year Ended June 30, 1900--Twenty-First Annual Report of the United States Geological Society. ving been individuallyseparated into segments by parting planes perpendicular to their mainaxes (.see PI. 111). In the small neck shaped hill one-fourth of amile northwest of Pompt^raug Valley Station the upper surface of theexposure is crossed by thin silica veins to form a honeycomb-likenetwork, suggesting that prismatic jointing cracks have here Ijcensubsequently healed by infiltration of silica. It is not uncommon to find numerous minute elongated lenticularcavities in the basalt of this .sheet, these vesicles Ijeing generally linedand partially filled with brown iron oxide. In contrast with the western belt of the main basalt sheet, the east-ern one is characterized ])v coarse vesicular structure, spheroidalparting, and, what is doubtless the natural consequence of these openstructures, greater decomposition and disintegration. In comparisonwith the anterior basalt .-heet, the vesicles of the main sheet are gen-erally larger but less numerous, and it is generally, but not always,. HOBBs] RELATIONS OF NEWARK TO BASEMENT FLOOR. 47 easy to distinguish specimens from the two sheets on this Thefresher appearance of the main basalt, however, aids in this determi-nation. The same tendenc}^ to cover its slopes with chips of weatheredrock which was noted in connection with the anterior sheet is also to beobserved here. The spheroidal parting is often very beautifully shown in exposuresof this sheet—e. g., at the road corner northwest of the Oak TreeHouse at Southbury. It is best observed, however, on the right(western) bank of D. M. Mitcheirs brook, just above the main bendand below the Stiles shale pits and due east of the Triangle. The cavities, which in the basalt of the southeastern areas vary fromelongated lenticular vesicles filled with brown oxidation products toamygdules the size of a pea or lar
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