312 H. C. COOKE 



from the usual altered basalt. This is particularly the case in the 

 area about 2 miles due north of Larder Village. But careful 

 detailed examination showed that nowhere are there any elhpsoidal 

 structures or amygdaloidal or other textures characteristic of 

 lavas, although the massive character of the rocks indicates that 

 these textures would have been preserved had they ever existed. 

 On the contrary, bedding was observed at many points where 

 exposures were clean and free from moss. Stratification is rarely 

 prominent, but always distinct, being marked by slight changes in 

 color, composition, and grain. It was clear therefore that these 

 rocks are not lavas, but greywackes, presumably composed of the 

 debris of eroded basalt flows. This conclusion was strengthened 

 by finding in many places on clean weathered surfaces occasional 

 angular or subangular grains of basalt. 



Since these rocks are thus proved to be sediments, not lavas, 

 the earlier conclusions as to the interbedding of the Larder Lake 

 sediments with lavas become invalid, together with the conclusions 

 drawn therefrom as to the Keewatin age of the sediments. As 

 there is no observed unconformity between the different bands of 

 sediments, it is concluded that they form a single series, infolded 

 with the older volcanics into a tight synchne. This series of 

 sediments rests unconformably on the Keewatin, since the basal 

 conglomerate is composed mainly of Keewatin material, and is 

 overlain with structural unconformity by the Cobalt series. It 

 is intruded by feldspar porphyries and by lamprophyre dikes. 

 Because of its stratigraphic position, lithological similarity, and 

 geographic continuity (Fig. 3) the series is clearly a continuation 

 of the Kirkland Lake Timiskaming. 



Figure 3 shows the Timiskaming to be a strong band i| to 2 

 miles in width, with a general east-west trend. Less than 3 miles 

 due east of where the band is concealed by the Cobalt series on 

 the east side of Larder Lake, the Pontiac series outcrops, and con- 

 tinues as a strong band for another hundred miles eastward. 

 J. A. Bancroft has shown that the external relations of the Pontiac 

 series are identical with those of the Timiskaming series; both 

 overHe the Keewatin with unconformity, are intruded by granites, 

 and are overlain by the Cobalt series with great unconformity. 



