THE RIFTED RELICT-MOUNTAIN, A TYPE OF 

 " OLD RED " OROGENY 



BY JOHN M. CLARKE 



Theme. Mountains of " Cat skill" type and age have generally 

 been regarded as plateaus or mesas downcut by rejuvenated drain- 

 age. It is probable that their isolation as mesas is due to the rifting 

 of their sides by solution of the underlying pavement, especially 

 where the latter is calcareous. 



The Catskill mountains of New York, an elevated and much dis- 

 sected plateau of horizontal rocks, are now interpreted as a deposit 

 made largely in the deltas of the streams which were the drainage 

 outflow from mountains at the east whose roots alone are known 

 to us as the hills and ridges of southern New England. This con- 

 ception of the origin of the Catskills as a continental rather than a 

 marine deposit, formed at the edge of the continent where fresh 

 waters were pouring into the salt, is an old one which has 

 gradually worked itself into general acceptation from data ac- 

 cumulated from many sources and at the hands of many investi- 

 gators. The additional conception that it is the accumulation of 

 land wash from the degradation of now wasted mountains at 

 the east is one that we owe more explicitly to the recent work of 

 Professor Barrell. 



The geological age of the Catskill formation in the Appalachian 

 region as a whole has been quite uniformly regarded as covering 

 the final term of Devonic time, and there has been no conclusive 

 evidence adduced as yet that this terrestrial sedimentation ignored 

 the conventional marine boundaries between the Devonic and the 

 Carbonic. The writer has at one time or another expressed 

 the belief that, so far as the Catskills of New York are concerned, 

 a coordination of deposits of this " Old Red " type would indicate 

 the fact that the Devono-Carbonic marine time boundary line was 

 actually transgressed in this deposition and that the upper part of 

 the original Catskill sedimentation in New York, whether or not 

 any trace of it remains from the subsequent dissection of the 

 Catskill plateau, was deposited in post-Devonic times. This inter- 

 pretation was suggested in the first place from a study of the so- 

 called " Catskill " deposits of the southern counties of New York- 

 west of the general area of maximum Catskill sedimentation and 

 at a time when it became necessary to subtract from what had been 



