of the St. Francis Valley, Quebec. 73 



the St. Francis river in the town of Richmond, or the village 

 of Melbourne. Perhaps better evidence still is to be found in 

 the banks of the little post-glacial gorge of the " eddy " brook 

 in Melbourne. Here in a height of about thirty feet the rock 

 passes from typical black limestone in the bed of the stream 

 to black mica schist at the top of the northern bank, which 

 owes the steepness of its slope in some measure to the differ- 

 ential resistance to erosion in the various strata exposed in it. 

 Somewhat similar phenomena can be seen in the Gushing brook 

 in Richmond, where, however, the banks are not as high. In 

 both cases the strata dip towards the north-northwest at an 

 angle of probably less than 30°. On the western bank of the 

 St. Francis river* the black mica schist, which forms the transi- 

 tional beds between the black limestone and the gray mica 

 schist, contains interbedded lenses of quartzite, an association 

 that is common in another part of the section where these two 

 rock varieties have their chief development. The gradual 

 passage of mica schist into micaceous dolomite and of the lat- 

 ter into quartzite has been already mentioned. Hence it 

 appears conclusive that the stratified rocks of this section 

 belong to a single cycle of deposition. 



With regard to their relation to the igneous rocks in point 

 of age, the balance of evidence thus far obtained indicates that 

 both igneous masses are older than any of the intervening sed- 

 iments. At the south the evidence is not conclusive, being 

 wholly negative, viz., the absence of dikes, contact metamor- 

 phism, springs along the contact, or other phenomena charac- 

 teristic of an intrusive contact. On the north the case is a 

 clearer one. Besides negative evidence similar to the above, 

 the dolomite where it approaches the trap in the township of 

 Melbourne holds fragments of the latter rock. Also the gray 

 mica schist on the line of section shows a marked increase in 

 the amount of chlorite which it contains as the trap hills are 

 approached. This is so noticeable as to make the rock diffi- 

 cult to distinguish from the trap in the field near the contact. 

 As the latter is a rock that reduces to a fine debris of which 

 chlorite is the most conspicuous mineral, this phase of the mica 

 schist appears to have derived its character from the residual 

 material of the trap. It is thus equivalent in evidence to a 

 basal conglomerate. 



The dip is naturally regarded as an observation of, at most, 

 very doubtful value in such a highly disturbed region, unless 

 corroborated by other evidence. 



In stratification all the rocks on the north of the black 

 limestone appear to dip towards the northwest, and those on 



* The old ferry landing at the rear of the residence of Mrs. J. Dunbar. 



