314 H. C. COOKE 



structure of the latter causes them commonly to assume the form 

 of sills. Gold deposits have not as yet been found around the 

 batholiths, presumably because the upper contacts, where juvenile 

 waters might have deposited ores, have been eroded away, while 

 the lower surfaces are not exposed. The porphyry dikes fre- 

 quently have gold deposits associated with them, but it is com- 

 monly found that such deposits are small, presumably because the 

 dikes are not large enough to have afforded any great amount of 

 juvenile water. The most favorable form for the porphyry to 

 assume would seem in theory to be the sill, which combines a large 

 volume with a relatively small thickness, together with the expo- 

 sure of both edges, in tilted rocks. The facts correspond with the 

 theory, inasmuch as within the boundaries of the Timiskaming 

 series, where the porphyries commonly form sills, gold discoveries 

 have been very numerous, and many of the discoveries have been 

 developed into producing mines. 



The syenite porphyry is found in large amount throughout the 

 Kirkland and Larder Lake districts, and was found by the writer 

 in Quebec, to the east of the Larder Lake area, and also on Lake 

 de Montigny, near the east end of the Pontiac area. It would 

 seem likely therefore that it may be found intruding the Timiskam- 

 ing series throughout its whole length of 130 miles although perhaps 

 not in such volume as in the Kirkland and Larder areas. Thus 

 the correlation between the Timiskaming and Pontiac series 

 increases the Timiskaming area, already recognized as very favor- 

 able for prospecting, to four times its former known size. 



EXTERNAL RELATIONS OF THE TIMISKAMING SERIES 



Facts already briefly stated in the foregoing pages indicate 

 that the Timiskaming series overlies the Keewatin unconformably, 

 is intruded by granitic rocks, and is overlain with great uncon- 

 formity by the Cobalt series. In view, however, of the disagree- 

 ment that has existed in the past between those studying the 

 districts under consideration, it seems advisable to enlarge some- 

 what on the previous statements. 



Relations to the Keewatin. — The basal conglomerate of the 

 Timiskaming series contains pebbles of all the volcanic series, as 



