252 
ANNALS NEW YORK ACADEMY OF SCIENCES 
Folds and Faults 
These formations are everywhere folded into a succession of anticlines 
and synclines whose axes trend northeastward. They have also suffered 
extensive erosion, so that the crests of all the anticlines are truncated, 
with the result that in the present areal distribution these formations lie 
side by side in long relatively narrow belts. The axes of these folds are by 
no means straight for any great distance, neither are they horizontal. In 
general, all of the folds pitch southward at gentle angles and take occasional 
bends. Therefore in passing southward, whether on an anticline or in a 
syncline, higher and higher formations or beds are met with. So it happens 
that on Manhattan Island the Manhattan Schist, the highest member, 
increases in areal distribution until it covers most of the width of the island. 
But everywhere, unless there has been some additional displacement, there 
is a belt of limestone between the schist and gneiss. Most of the folds are 
unsymmetrical, and sometimes they are overturned. 
Both longitudinal and cross-faults occur, but there is no doubt that the 
former are of most prominence. In the East River at Blackwell’s Island 
almost the whole thickness of Inwood Limestone, which should be found 
between the schist and gneiss, is lacking. The residuary matter and con¬ 
dition of the bed rock, as shown in the Seventieth Street tunnel of the East 
River Gas Company, indicates crushing and much decay, such as should be 
expected in a fault zone, and there is every reason to regard it as a fault. 
Doubtless there are others of similar displacement, but their relations are 
such that the effect is too obscure to be readily seen. Numerous weak 
zones of a similar sort run across the formations in a general northwest- 
southeast direction. It is probable that most of them represent actual cross 
faults. The throw is probably not great in any case, and the off-set is 
usually insignificant. These zones, however, control the distribution of 
cross valleys, some of which, like the Manhattanville Valley, are among 
the most striking features of the island. 
A real D istrib ut ion 
All the formations lie beneath the drift in more or less regular belts,— 
narrow if closely folded, or comparatively wide if more gently folded,— and 
with a northeasterly strike. The Inwood Limestone lies normally between 
a schist belt and one of gneiss and is usually narrow. It always holds this 
position unless cut out by faulting. 
Irregularities in distribution are common. They are chiefly of the nature 
of bends in the course or strike of the formation, a widening of the belt 
locally, a disappearance or an emergence due to cross-folding or local 
