Inzijood Li))icstonc of ManJiattait Island. — Eckel. 123 
The limestone exposed on Hawthorne St. is a comparative- 
ly fine-grained dolomyte, with small amounts of a brown mica, 
and frequent crystals and incrustations and interlaminations of 
chalcopyrite. Tremolite is infrequent, although a block fur- 
ther east extremely large and fine crystals are common. Small 
veins and stringers carrying quartz, often in crystals, cut the 
limestone in many places. The limestone is distinctly and 
rather heavily bedded. The layers have a line of strike about 
17° east of north, dipping about 30° to the east. The pitch 
is very high, being 30° to 40° to the southwest. The steep- 
ness of the pitch and the fact that the strike approaches more 
closely to the north than is common in this section, would 
seem to indicate that we are near the southerly end of a fold; 
on its westerly side. It will later be shown that this fold is 
probably synclinal. 
As shown in the sections, the limestone is cut in several 
places by an intrusive. This rock is a coarse grained pegma- 
tyte, consisting of quartz and orthoclase, with a very little 
muscovite. Black tourmaline is a rare accessory. At the 
north end of the western side of the street, a main sheet, six 
feet thick, of pegmatyte, gives rise to a large number of smaller 
stringers. In these, and in the adjoining limestone, brown 
tourmalines are developed, generally in radiated clusters. 
Though this occurrence is most distinct here, it is repeated 
to a greater or less extent at other contact points. The con- 
tact plane between limestone and pegmatyte is everywhere 
marked by the development in the former, for a depth of an 
inch or so, of small tremolite crystals and a great profusion 
of biotite in fine scales. These give a gray or greenish tint 
to the limestone in this narrow band. 
The pegmatyte, in sheets varying from a foot up to twelve 
feet in thickness, cuts the limestone generally transversely to 
its bedding planes, but occasionally parallel to them. In all 
cases, however, the intrusive sheet follows very closely the 
pitching plane of the limestone. An exception to this rule 
may occur at the southerly end of the east side of the street, 
where a mass of pegmatyte, thirty feet in thickness, is exposed 
at the contact between limestone and gneiss. This mass has 
been so far excavated as to render difficult a determination 
of its exact form, and of its relation to the gneiss. The peg- 
matyte may enter the gneiss, but there is no clear proof that 
