FORMATIOXS OF THE SKUNNEMUNK MOUNTAIN" REGION 45 



in the east cut where its thickness is 40 feet. This probably 

 represents the entire thickness, as the upper portion begins to 

 show New Scotland characteristics. The upper part is a very 

 coarse, porous, cherty limestone and contains abundant fossils. 

 The lower part is not so cherty and has more of the aspect of 

 the Manlius, though it also has many fossil remains. Near the 

 base of the formation the rock contains fragments strikingly 

 similar to the Manlius. This is of special interest as the base 

 of the Coeymans marks the lower limit of the Devonic. Other 

 outcrops of the Coeymans can be seen near the highway which 

 crosses this formation farther south. It also shows in some 

 excavations that have been made for limonite and in a small 

 •quarry south of the highway above mentioned. A little beyond 

 this quarry the Coeymans and all the lower formations down to 

 the Longwood shales are cut off by faulting. 



Manlius limestone. This formation has a thickness of 7 feet. 

 It here appears as a massive limestone, but otherwise has the 

 features of the Manlius. The thinness of the formation in this 

 section is unusual and from the fact that the base of the Coey- 

 mans contains fragments of what appear to be Manlius and also 

 from the small thickness one is led to believe that the upper 

 part of the Manlius has been eroded before the deposition of 

 the Coeymans. The studies of Dr Grabau 1 at Becraft mountain 

 indicate that the change from the Manlius to the Coeymans was 

 a gradual one. Similar results have been reached by the study 

 of the Manlius in New Jersey and central New York. Van 

 Ingen and Clark 2 give evidence to show that the Manlius was 

 •slightly eroded before the deposition of the Coeymans. Fossils 

 are rarely found in the Manlius as exposed in the cut. Holo- 

 pea antiqua Vanuxem is the most characteristic, while 

 Leperditia alta Conrad and Tentaculites gyra- 

 c a n t h u s Eaton are occasionally seen. The Manlius extends 

 south to the fault previously mentioned. The contact with the 

 Coeymans may favorably be seen in a small quarry south of the 

 riighway. The Manlius has not been observed in the west limb 

 of the syncline. 



Rondout formation. This is rather a massively bedded lime- 

 stone with some thin partings of shale. The formation is 13 

 feet thick and at about the middle there is a very sandy layer 

 about 1 foot thick. This layer shows cross-bedding and 

 although slight it is very distinct. The upper part of this for- 

 mation shows the distinctive sun cracks of the Rondout as 



*N. Y. State Pal. An. Rep't. igo2. p. 1052-54. 

 • 2 N. Y. State Pal. An. Rep't. 1902. p. 1186. 



