EXFOLIATION DOMES IN WARREN COUNTY, 



NEW YORK 



BY W. J. MILLER 

 INTRODUCTION 



While engaged in geological work in Warren county during the 

 past summer the writer was impressed by the fact that the most 

 striking feature of the landscape, especially on the North Creek 

 sheet and certain portions of the Luzerne sheet, is the prevalence of 

 distinct, isolated, domelike, topographic forms which rise hundreds 

 of feet above the comparatively low land of the region. A compari- 

 son of the North Creek sheet with all other published Adirondack 

 maps shows that, from the physiographic standpoint, this region is 

 noticeably different from the Adirondacks in general. One would 

 scarcely think of such a very ancient region of comparatively low 

 altitudes as being favorable to a widespread development of exfoli- 

 ation^ domes and it is the purpose of this brief paper to call atten- 

 tion to these forms and to show how several factors have conspired 

 to favor their formation. The paper is concerned more especially 

 with the North Creek and Luzerne topographic sheets which the 

 reader is expected to consult. 



GENERAL GEOLOGIC FEATURES 



The region lies wholly within the Precambric rock area of the 

 Adirondacks. The oldest rocks are the highly metamorphosed sedi- 

 ments of the Grenville formation. Detailed mapping, now in prog- 

 ress by the writer, shows that the Grenville is very extensively 

 present and that crystalline limestone is unusually prominent in 

 the formation. Next in age come plutonic igneous rocks such as 

 syenite, granitic syenite, and granite porphyry which are clearly 

 intrusive into the Grenville, and all of which are differentiation 

 products from the same cooling magma. 



Of the igneous rocks, the syenite is, perhaps, the most abundant 

 and is generally quartzose and hornblendic with a more basic vari- 

 ety carrying a green pyroxene. The rock is medium to coarse 

 grained, greenish gray when fresh and weathers brown. The 

 granitic syenite is highly quartzose and generally carries horn- 



^ The term exfoliation is here employed in the usual sense and means the 

 splitting off of the surface portions of rock masses in large sheets as a result 

 of temperature changes. 



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