[MATTHEW] GEOLOGICAL CYCLES IN MARITIME PROVINCES 123 



Ftones (No. 4), which, with the intervening memher (No. 3) show the 

 passage of an old sedimentary series from rathei shallow water condi- 

 tions, to the deeper waters of an open sea, comparatively free from 

 sediment. 



In comparing the series with the corresponding one in Cape Breton, 

 the intrusions of igneous rocks there are even more confusing than at 

 St. John. However, a section at Crane Brook^ presents some of the 

 main features of the succession; numbers 5-11 of that section show 

 about 600 feet of quartzites; numbers 13 to 16 intrusions that separate 

 the quartzites from the limestones; the limestones themselves (in Nos. 

 17 to 30) are greatly broken up by intrusive syenite, etc., but show 

 over 200 feet of limestones and dolomite, exclusive of spaces where the 

 measures are concealed. 



St. John is evidently the best point at which this old cycle of 

 sedimentation may be studied, though even here its base cannot clearly 

 be made out, without more careful study than has been devoted to it. 

 In the quartzites we find sediments like those of the lower part of the 

 gold bearing rocks of Nova Scotia; in the overlying silicious dark 

 argillites the condition which supervened when the sea-bottom sanlv so 

 far as to be out of reach of strong currents; in the limestones a con- 

 tinuance of similar submergence, but with clearer ocean waters and 

 probably a higher temperature; and in No. 5 a recurrence of clay beds 

 (with diorite flows) may indicate the approaching elevation of the sea- 

 bottom which terminated this cycle of sedimentation. It at least in- 

 dicates a temporary reversion to conditions resembling those that pre- 

 vailed when No. 3 was deposited. The prevalence of earthy graphite 

 and the abundance of sulphurets distributed in No. 5 may lead one to 

 surmise the existence of abundant organisms of low order at this time. 

 In these respects No. 5 resembles the upper member of the Lower 

 Huronian, and also the upper part of the succeeding Cambrian ( Cambro- 

 Ordovician) terrane. 



This old cycle is of interest from several points of view. It is 

 the only one in all this eastern region which exhibits large masses 

 of limestones, except the Lower Carboniferous; hence, where it occurs 

 it may be used with confidence as a stratigraphical unit in determin- 

 ing the presence of a definite horizon, even where overlying palœozoic 

 terranes cannot be determined for lack of palseontological data. 



Another feature of this cycle is the peculiar condition of the 

 intnisives, of which there are large masses. They do not have the 

 bright crystalline aspect of the crystalline intrusives of the later ter- 

 ranes, but are often notable for the changed condition of the magnesian 



*Rep. Prog. Can. Geol. Surv., 1875-76, p. 386. 



