46 NEW YORK STATE MUSEUM 



sediments of the Shawangunk range and the Catskills above, lies 

 a series of quartzites, limestones and slates less complexly dis- 

 turbed than the older and more disturbed than the younger series 

 — set off from both by unconformities representing time intervals 

 that cover both folding and erosion. They are of more than 4000 

 feet thickness — how much more it is impossible to estimate be- 

 cause of the obscurity of data in the slates. There are very few 

 fossil forms preserved in them. The series is, however, readily 

 and sharply separable into three formations that may be mapped 

 upon lithologic characters alone. They are of most importance in 

 the Wallkill valley, Moodna creek, Newburgh, Fishkill, New Ham- 

 burg and Poughkeepsie districts. Their character, structure, and 

 conditions have required careful consideration in the decisions on 

 the Wallkill and Moodna siphons and in the discussions on the 

 proposed Hudson river crossings [see Hudson river crossings, 

 pt 2]. 



(22) Hudson River slates. The upper member of the Cambro- 

 Ordovicic series is in itself complex. Prevailingly it is a slaty 

 shale, occasionally it is a sandstone or shaly sandstone, or a simple 

 shale; still more rarely it is almost a true slate, and very rarely 

 a phyllite. The constituents vary from prevailing clay to quartz 

 sand repeatedly in almost every locality. It is probable that as a 

 rule the upper portions are the more heavily bedded and arena- 

 ceous. The rock is excessively affected by the dynamic movements 

 that have at least twice disturbed it. A slaty cleavage in the more 

 argillaceous members is most noticeable, but almost everywhere the 

 strata are strongly tilted, crumpled, broken, faulted, or crushed in a 

 most confusing way. This together with an original obscurity 

 in bedding, and the obliteration by subsequent shearing of much 

 that did exist, makes it impossible to reconstruct the complicated 

 structure or compute the thickness of the formation. It is of such 

 physical character as to absorb within its own limits much of the 

 disturbing movements, and neither the formations above nor imme- 

 diately below are so extensively and intimately affected. The 

 formation is widely exposed and forms the bed rock over very large 

 areas. Almost everywhere it is impervious to water, easy to pene- 

 trate by drill or tunnel, and resistant to decay. A few Ordovicic 

 fossils may be found, the most characteristic being D a 1 m a n e 1 1 a 

 testudinaria. 



(23) Wappinger limestone} (In part Cambric, and in part 



1 The Wappinger Valley limestone of Dwight (1879) and Dana. The 

 Wappinger limestone of Darton and others. 



