ABSTRACTS OF PAPERS 127 



Presented extemporaneously, with the aid of lantern slides. 

 Discussed by B. K. Emerson and L. C. Graton. 



GRAPHIC STUDY OF IGNEOUS ROCK SERIES 

 BY FRANK F. GROUT 



The paper is to be published in full in this volume of the Bulletin. 

 Presented by title in the absence of the author. 



MOUNT MONADNOCK, VERMONT — A MONTE REG1 AN HILL 

 BY JOHN E. WOLFF 



(Abstract) 



Mount Monadnock lies at the west bank of the Connecticut River, in Ver- 

 mont, 6 miles sbuth of the Canadian boundary and opposite the town of 

 Colebrook, New Hampshire. The mountain is oval in plan, three and a half 

 miles in longer diameter ; elevation of summit, about 3,140 feet above tide and 

 2,000 feet above the river at its base. An intrusive mass of alkali-syenite 

 forms the major part of the mountain; the rock is composed essentially of 

 micro-perthite, quartz, albite, hornblende, biotite with granitic or quartz-rich 

 and basic phases. At least one mass of essexite is found deep in the dissected 

 core, and there are camptonite, aplite, and bostonite dikes cutting the syenite. 

 The country rock is a fine-grained micaceous quartzite or quartz-schist, which 

 the igneous mass truncates as a stocklike intrusion. There is no published 

 map of the mountain and only a brief mention of the geology in Hitchcock's 

 Geology of New Hampshire. Lantern slides will show maps of the mountain 

 and distribution of all the Monteregian Hills, and the appearance of the 

 mountain and Connecticut Valley from several sides. 



Presented without notes, with lantern-slide illustrations. 

 Discussed by F. D. Adams, H. S. Washington, J. A. Dresser, Arthur 

 Keith, and E. 0. Hovey, with reply by the author. 



Discussion 



Professor Adams: Dr. Wolff's paper is of much interest, both as affording 

 a general view of the Monteregian Hills of New England and a description 

 of a new member of this petrographic province in northern Vermont. Speak- 

 ing generally, the Monteregian Hills in Canada show a progressive increase 

 in basicity from east to west, and the more acid character of the hills of 

 New England seems to indicate that this change is continuous into the United 

 States. I ask whether, in addition to the main intrusions of Mount Monad- 

 nock, there were many dikes. In Canada there were only two of the Monte- 

 regian Hills which showed any considerable number of them, namely, Mount 

 Shefford and Mount Royal. About the latter both the surrounding country rock 

 and the intrusions themselves were traversed in all directions by great swarms 

 of dikes. Seven sets of these, each cutting the preceding set, were found in 

 the reservoir extension of Montreal. A great deal of light has been thrown 



