128 PROCEEDINGS OF THE AMHERST MEETING 



on the successive stages of volcanic activity of Mount Royal by a careful 

 study made by Dr. Bancroft of the exposures laid bare by driving a tunnel 

 through this mountain recently by the Canadian Northern Railway for the 

 purpose of gaining access to the city of Montreal from the north. In this the 

 successions, not only of the main intrusions, but also of many sets of dikes, 

 have been determined, as well as the existence of extended alterations and 

 new deposits due to vapors and waters given off in the final stages of the 

 volcanic activity. 



Mr. Dresser : I would join in commendations of Dr. Wolff's very interesting 

 paper and ask a single question. Of the Monteregian series of Quebec, only 

 two of the hills, Mounts Royal and Shefford, on the extreme east and extreme 

 west, show a notable development of dikes. The same two hills give strong 

 presumptive evidence of laccolithic structure. Has Dr. Wolff observed evi- 

 dence of laccolithic structure in Mount Monadnock in which dikes are 

 abundant? 



Dr. Hovey called attention to an acid dike cutting diabase of New Haven 

 region described by him and analyzed by H. S. Washington. 



Reply by Author : In connection with questions as to the possible age of 

 the intrusion, the author mentioned a dike of monchiquite described many 

 years ago by L. S. Griswold as cutting one of the Triassic trap sheets of 

 Connecticut and probably satellitic to the alkaline intrusions of the Novang- 

 lian petrographic petrovince. 



GEOLOGY OF THE PAWTUCKAWAY MOUNTAINS 

 BY EDWARD S. C SMITH a 



(Abstract) 



The Pawtuckaway Mountains are a group of three well glaciated hills of 

 the residual type, ranging from eight hundred to one thousand feet in altitude 

 above sealevel, lying in Rockingham County, New Hampshire, 22 miles west 

 of Portsmouth and 10 miles northeast of Manchester. 



They consist of the remnants of a deeply eroded igneous body of alkali 

 syenite which is intrusive into a more or less granitic gneiss of undetermined 

 age. The syenite is composed of microperthite, andesine, hornblende, pyroxene, 

 and biotite essential, with quartz, magnetite, apatite, and zircon accessory. 

 With the syenite occurs also a series of camptonite, tinguaite, and aplite 

 dikes. The camptonite forms a considerable portion of the central part of 

 the mass as well as appearing as dikes, while the other types are present only 

 in subordinate amounts. 



Another feature of interest is the rapid weathering of the syenite, which 

 has formed large dunelike deposits of its disintegration products, an unusual 

 sight in New England. 



Read bv J. E. Wolff in the absence of the author. 



1 Introduced by J. E. Wolff. 



