. Annals of the New York Academy of Sciences. Science; Science -- New York (State). 46 ANNALS NEW YORK ACADEMY OF SCIENCES These cases were all found in the two eastern areas, although less pro- nounced ones occur in the Montrose Point district. All of these rocks would be classed by Williams as augite peridotites (picrites) which he thought occurred in the highest development on Montrose Point. He describes at considerable length another group from Stony Point, how- ever, which is. not typically represented in the main area—the hornblende peridotites. The nearest approach to these rocks is to
. Annals of the New York Academy of Sciences. Science; Science -- New York (State). 46 ANNALS NEW YORK ACADEMY OF SCIENCES These cases were all found in the two eastern areas, although less pro- nounced ones occur in the Montrose Point district. All of these rocks would be classed by Williams as augite peridotites (picrites) which he thought occurred in the highest development on Montrose Point. He describes at considerable length another group from Stony Point, how- ever, which is. not typically represented in the main area—the hornblende peridotites. The nearest approach to these rocks is to be found in the hornblende pyroxenite area on the south side of Montrose Point; but these contain olivine to the extent of more than one-third only exception- ally. Oddly enough, however, Williams, who, after all, studied only a small part of the whole area, felt that they were so important a member of the Cortlandt Series that he proposed the name "Co^tlandtite,' for them, and rocks consisting of olivine and hornblende are now widely known by this name. A rather extraordinary rock, some- what analogous to the so-called cort- landite, does, however, occur in a small patch on the extreme eastern edge of the series. This in the hand specimen exhibits the poikilitic structure par excellence, but biotite,. instead of hornblende, is the host. This occurs in individuals often sev- eral inches across (although by rea- son of the abundance of the included minerals, it makes up somewhat less than one-third of the rock), and under the microscope it is extraor- dinary for the abundance of its inclusions. These are of a sharp, brownish black substance, probably magnetite, and are so abundant in the center of the grain as to render it opaque, but the periphery and a margin around each included olivine is entirely clear. On the extreme edge of tbe biotite in the latter case, however, there is a narrow band of magnetite grains, and surrounding, or nearly surrounding, the olivine is a
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectscience, bookyear1879
