318 BULLETIN OF THE 



west are hardly seen here, but the fine, massive hmestone was very pos- 

 sibly largely derived from a coral reef not far distant. There was no 

 good place to estimate its thickness ; but twenty-five or thirty feet, as 

 given by Emmons, seems too small. The margins of this formation have 

 a peculiar way of weathering out into large loose blocks, often ten feet 

 cube; good examples are seen on Old Kings road just south of the 

 Mountain road ; near Van Luven's Lake ; and north of Hooge Berg. The 

 last-named point gives a good section of the limestone at its southern 

 end, and it can be well seen at Leeds' west of the Grits. 



The Marcellus shale follows by a very abrupt transition, as may be 

 seen at its only exposure, on the east bank of the Cauterskill, just south 

 of the Mountain road bridge. It is a fine black fissile shale, in which a 

 few faint fossil shells were found in 1877. Its upper limit and thickness 

 were not determined, as it is throughout worn down into a valley be- 

 tween the Corniferous on the east and the Hamilton on the west, and 

 deeply buried under stratified clays. The Hamilton sandstones and 

 shales and the overlying formations were not examined closely ; the 

 lower layers of the former are well shown at the Big Falls of the Kaa- 

 terskill, where several strata are very fossiliferous ; Spirifer mucronata 

 and medialis are both of common occurrence. From the Marcellus val- 

 ley to the foot of the mountains these and similar, but non-fossiliferous, 

 sandstones and shales continue with a gentle westerly dip, and their 

 thickness must amount to over two thousand feet. From the foot of the 

 mountains to the summits of their broad masses, the strata are essen- 

 tially horizontal, and may measure about three thousand feet more, 

 chiefly of sandstones and sandy shales, with some conglomerates near 

 the top. These are generally accounted of the Catskill formation. 

 Cross-bedding is common throughout, and in a great part of the Hamil- 

 ton group. 



The most interesting question presented by this series of rocks turns 

 on the absence of the Medina, Niagara, and Salina strata from between 

 the Hudson River and the Lower Helderberg formations, and the possi- 

 bility of unconformity at this point of the section. The following his- 

 toric review will show what observations have been made and what 

 views have been held on this subject hi the Hudson valley. 



W. W. Mather. Report of W. W. Mather, Geologist of the 1st Geologi- 

 cal District of the State of New York. Albany, 1838. (2d Annual Re- 

 port.) "Mount Bob and Becraft's Mountain are outliers of limestones, 

 lying unconformably upon the subjacent slate rocks. I have traced these 

 rocks within a few feet of their junction in many places." (p. 165.) 



