Hornblende Lanvprofliyre Dyke at Richmond, P.Q. 315 



A Hornblende Lamprophyre Dyke at 

 Richmond, P.Q. 



By John A. Dresser, M.A. 



A trap dyke of considerable interest was lately discov- 

 ered by Mr. G. H. Pierce, C.E., in the lower Trenton lime- 

 stones on the southern outskirts of the town of Eichmond, 

 P.Q. It can be seen near the highways a few yards south 

 of the residence of Mr. Mills Wilcocks, having been 

 brought to view somewhat recently by the erosive action 

 of a small stream in the bed, or bank, of which it can be 

 traced for some twenty rods. 



It has a width of about three feet, and stands nearly 

 vertically, running in a southeast-northwesterly course 

 at an angle of 30° to 40° with the strike of the enclosing 

 sedimentary rock. This, which is a dark, nearly black, 

 graphitic limestone, belonging to what is known as the 

 Farnham Black Slates (Ann. Eept. Geol. Survey of Canada, 

 1 394, Part J, Dr. P. W. Ells) is not altered in any note- 

 worthy manner at the contact ; and while it has been 

 folded and contorted to a remarkable degree, being within 

 the folded belt of the Appalachian mountain system, the 

 dyke shows no evidence of having been subjected to the 

 same disturbing agencies. It has thus apparently been 

 intruded not only later than the deposition of the lower 

 Trenton sediments but after they had passed through the 

 crumpling, folding and tilting which has given them their 

 present altered character and position. 



The dyke is a fine-grained holocrystalline rock, having- 

 a dark iron-gray color and weathering readily on exposure 

 to a rusty brown. It is quite strongly magnetic, frag- 

 ments as large as grains of rice adhering readily to a 

 pocket horse-shoe magnet. 



