No. 10. — The Folded Ildderbcrg Limestones Hast of the Catsldlls. 



By William Mokris Davis. 



Intro(luctory. — Previous Descriptions. — Character and Sequence of tlic Formations. 



Hudson Mver Group. — Absence of Medina ^Niagara Group. — Waierlmu and 



Tentamlite. — Lower Fentmnerus Limestone. — Calskill Shaly Limestone. — Uncri- 

 nal and Upper Pentainerus Limestone. ~ Oriskany. — Gornifcrous Grits. — Gornif- 

 erous Liinesione. — Marccllus Shale. — Hainilton and Catskill Sandstones. — The 

 Question of Unconformity. — Paleogeography. — Folds and Faults. — The Catskill 

 Gorge below Leeds. — Other Points for Observation. ~~ Unconformity by Faulting. — 

 Gompression in Synclinals. — Gompression in Faulting. — Surface Geology. — Gla^ 

 cial Phenomena. — Stratified Glays. — Former Lines of Drainage. 



The Appalachian district in Pennsylvania is made up of three well- 

 distinguished parts : a plateau of nearly horizontal rocks on the north- 

 west, showing no formation younger than the Carboniferous and Upper 

 Devonian ; a rolling low country on the southeast, where the rocks are 

 Lower Silurian and older, greatly folded and often half or wholly crystal- 

 line ; an intermediate region, where the wave-like folds of the Paleozoic 

 strata arc best developed, and their effect in producing anticlinal, syn- 

 clinal, and canoe mountains is best seen. If we trace those three belts 

 northeastwardly into the Hudson valley, the fu'st is well shown in the 

 broad mass of the Catskills ; the second in the perplexing Taconic region 

 from the Hudson across to Western Connecticut and Massachusetts; 

 but the third, so striking in Pennsylvania, has dwindled to a narrow strip 

 of insignificant hills, only a mile or two wide, and a few hundred feet in 

 height. Although so greatly reduced in size, this middle belt still re- 

 tains its characteristic structiu*e very clearly, and reveals this structure 

 in its surface forms. The accompanying map represents a part of it 

 some ten miles in length, the middle point of which is about west of the 

 town of Catskill on the Hudson. Very little attention has as yet been 

 given to this belt of miniatvu"e mountains, excepting in the study of its 

 fossils. The following are the only descriptions referring to it that I 



have found. 



W. W. Mather. Geology of New York; First District. 'Albany, 

 1843, pp. 317-352, 3GG-421. A general description is given of tKe sev- 

 eral formations here occurring, their characters and sequence ; but the 

 structural peculiarities of the district are very imperfectly represented. 



VOL. VII. — NO. 10. 



