igoo-i.] Physical Geology of Central Ontario. 141 



Canada," is still the standard work of reference for the geology of 

 " Old " Ontario. Since 1863 there has been little work in the area under 

 the auspices of the Survey, except some work in 1886, the results of 

 which have not yet been made public. Both previous and subsequent 

 to Logan's summary there have been many shorter papers published 

 upon various topics. Some of these will be noted in the text. 



In the preparation of the present paper the writer has made use of 

 many sources of information, and due acknowledgment will be made 

 in the appropriate places. During the last few summers, as opportunity 

 offered, the greater number of localities referred to in the context have 

 been visited, and use has been made of the writer's own observations in 

 the field. 



The writer wishes to acknowledge his indebtedness to Mr. J. M. 

 Clarke, of Albany, for the identification of a number of fossils ; and to 

 Professor W. M. Davis, of Harvard University, for advice and criticism 

 while this paper was in preparation. 



Resume. — The area comprises, in all, about 6,500 square miles of 

 territory. Within its limits are found rocks ranging in age from the 

 Archean to the Niagara. These are overlaid by a great complex of 

 deposits dating from the Pleistocene epoch. Everywhere along the 

 northern boundary the various members of the crystalline series are 

 found passing beneath the Cambro-Silurian sediments ; in some locali- 

 ties outliers of the sediments are found upon the crystallines ; again, 

 inliers of the latter are found wholly or partially surrounded by the 

 former. At one time the sediments extended much farther towards the 

 north ; their removal has revealed ridges, valleys, and residual monad- 

 nocks, the sub-mature topography of a well-dissected plain of denuda- 

 tion, a plain long antedating the Cambrian. 



The basal members of the sedimentary series are destitute of fossils, 

 and consist of more or less coarse detritus ; above them thick deposits 

 of fossiliferous limestone were formed, and in many localities this 

 limestone rests directly upon the crystallines. These limestones are in 

 turn overlain by bituminous shales. 



A second cycle of slow depression, much greater than the former, 

 resulted in the formation of a similar series of deposits, the upper 

 members of which lie beyond the area under consideration. 



In the long interval from the close of the last period of deposition 

 within the area until the beginning of the Pleistocene epoch, during 



