2 54 FRANK D. ADAMS 



discussion of its origin, is now in press and will appear in the 

 Canadian Record of Science within the next few weeks. The other 

 four hills have not as yet been studied in sufficient detail to 

 enable any definite statement concerning their structure to be 

 made. 



In the Monteregian hills there are thus intrusions of the 

 nature of laccolites, true necks, and probably also of stocks. 

 The age of the intrusions cannot as yet be definitely determined. 

 They are later than the lower Devonian, for some of the dykes 

 connected with Mount Royal cut limestones which belong to the 

 summit of the upper Silurian, while fragments of limestone which 

 are shown by the fossils which they contain to be referable to 

 the lowest beds of the Devonian, occur as inclusions in the vol- 

 canic breccia or agglomerate which is found about the flanks of 

 the same mountain. The deeply eroded character of the moun- 

 tains, however, shows that they are of early date, and it seems 

 most probable that the intrusion took place somewhere in later 

 Paleozoic times. 



Having considered in a general way the character of the 

 Monteregian hills as a whole it may be of interest to look some- 

 what more closely into the structure and petrographical char- 

 acters of one member of the group which has recently been 

 studied in some detail, namely Mount Johnson. 



MOUNT JOHNSON. 



Mount Johnson rises from the plain twenty-two miles east- 

 southeast of the city of Montreal, and six miles northeast of the 

 town of St. Johns on the Richelieu river, and twenty-five miles 

 north of the international boundary. The little village of St. 

 Gregoire is situated near its base. The surrounding country is 

 perfectly flat, forming a fertile and well-tilled agricultural dis- 

 trict, the nearest mountain being Rougemont, which lies in a 

 northeasterly direction some nine miles distant. In cross-section 

 Mount Johnson is nearly circular. (Fig. 2.) The igneous plug 

 itself has at the base, immediately above the hornstone collar, a 

 somewhat elliptical outline and measures 3,500 feet by 2,500 

 feet, the longer axis having a direction N 20° E. This gives the 



