of the St. Francis Valley, Quebec. 71 



numerous enough to warrant calling the rock a conglomerate 

 in the usual sense of the term, yet they are quite distinct in 

 lithological character from the enclosing rock. One of these, 

 which occurs on Lot 15, Range xiii of the Cleveland, can be 

 seen to occupy not less than four hundred feet, and may be 

 considerably more extensive. Its thickness could not be 

 ascertained, but is not less than two feet. Similar occur- 

 rences of limestone are also found in the micaceous dolomite 

 and will be subsequently noted. 



As there is no evidence of concretionary structure they 

 must apparently be either fragments of an earlier and disin- 

 tegrated limestone bed, or calcareous deposits formed contem- 

 poraneously with the enclosing rocks. The absence of any 

 evidence of unconformity or other indication of a time-break 

 favors the latter view. 



Micaceous Dolomite. — The gray mica schist becomes dolo- 

 mitic in certain parts by the intercalation of lenses of magne- 

 sian limestone. These growing more abundant and the inter- 

 vening bands passing into an impure earthy magnesite, the rock 

 eventually becomes a crystalline dolomite. In the hand speci- 

 men it is fawn-colored and shows the presence of quartz on 

 the weathered surface. In the thin section it is made up of 

 crystalline dolomite with about one-quarter of the slide occupied 

 by quartz. The latter is generally well crystallized, showing 

 that it was formed not later than the dolomite. The debris of 

 a kiln where the dolomite was formerly burned for lime, as well 

 as decayed portions of the rock, yield considerable numbers of 

 well-formed, transparent quartz crystals. 



Lenticular masses of rich hematite ore carrying octahedral 

 crystals of magnetite occur in the dolomite at various places. 

 They are found several feet in thickness and are either over- 

 lapping or nearly continuous for distances of a mile or more. 

 Their close association with dolomite suggests their origin 

 from altered carbonates. 



The dolomite also contains pure limestone masses, as noted 

 above, one or which is of much importance from the fact that 

 it has long been known to contain fossils. This mass, which 

 is found on Lot 14 in Range xii of the township of Cleveland, 

 about three hundred yards east of the Healy schoolhouse, is 

 some two feet in thickness and thirty in length as exposed on 

 the face of a low escarpment of dolomitic mica schist. A cum- 

 munication from the late Sir William Dawson on the silicifica- 

 tion of these fossils appeared in the Quarterly Journal of the 

 Geological Society of London in the year 1879.* In this they 

 were referred to as of Lower Silurian age and the genera Steno- 



*"On Paleozoic Fossils mineralized with Silicates," Q. J. G. S., Feb. 1879, 

 pp. 60-62. 



