356 HENRY B. KUMMEL 
bluish-gray, many of them calcareous, and occur more commonly 
higher in the formation. The fine-grained rocks exceed the gritty 
beds. 
Slaty cleavage is the predominant structure of the fine-grained 
beds, and the true bedding planes are in many places difficult to 
determine. At some horizons the planes of cleavage are so straight 
and parallel and the rock so even textured that commercial slates 
have been obtained in considerable quantities. The whole forma- 
tion is so crumpled and: cleaved that no accurate estimate of its thick- 
ness can be made, but it is probably at least 3,000 feet, and it may 
be more. 
Four species of graptolites characteristic of the Normanskill fauna 
of New York have been found in the lower portion of the Martins- 
burg shale, so that the beds in which they occur are equivalent in 
age to the middle portion of the typical Trenton limestone of central 
New York. <A few miles north of the New Jersey state line, Schizo- 
crania and graptolites characteristic of the Utica shale of the Mohawk 
Valley have been found in beds close to the overlying Shawangunk 
. conglomerate. 
SILURIAN SYSTEM 
Contrary to long-prevalent, and apparently well-established belief, 
the lower and middle portions of the Silurian system are not repre- 
sented in New Jersey. ‘Their absence in this and adjoining regions 
is indicative of somewhat widespread earth movements unaccom- 
panied in this region by folding, which closed the period of deposition 
indicated by the Martinsburg sediments or possible overlying beds 
afterwards removed by erosion and raised the region above 
the zone of sedimentation. When deposition began again late in 
Silurian time, beds of coarse conglomerate were laid down, followed 
by sandstones, shales, and limestones, the earlier sediments being 
those of a low-grade delta in an arm of the Appalachian gulf. 
These conditions of deposition prevailed with but slight changes of 
elevation into Devonian time. 
Shawangunk conglomerate—The Shawangunk conglomerate (the 
Oneida conglomerate of many previous publications) is chiefly a 
«Clarke, N. Y. State Museum Bulletin 107, p. 303. 
