[KEELE] ■ MESOZOIC CLAYS AND SANDS 37 



The beds on Wabiskagami river are about two miles west of tiie 

 Missinaibi outcrops. The materials in both localities are alike, and 

 the deposits are very probably continuous, but the stony character 

 of the glacial drift overburden rendered it impossible to prox'e this 

 by boring. 



Sink holes and solution channels in limestone on Mattagami river 

 at Grand Rapids are partially filled with iron ore and clay and a small 

 quantity of lignite. The clays of some of the beds in the limestone 

 cavities are refractory enough to be classed as fire-clays, and it is 

 quite possible that the beds belong to the same period of deposition 

 as the clays and lignite farther south. These clays are 20 miles north 

 of the pre-Cambrian rock boundary. 



The known scattered remnants indicate that the Cretaceous clays 

 were once spread over an area at least 40 miles long and 20 miles 

 wide, and it is certain that they originally had a much larger extent 

 of country. 



The Cretaceous clays seem to be confined to the northern Palae- 

 ozoic plain, as no remnants have yet been found on the pre-Cambrian 

 upland to the south. It is probable, therefore, either that these 

 clays were not laid down at as high a level as that of the upland or 

 that the pre-Cambrian surface was swept bare of Cretaceous sediments 

 before Pleistocene times. 



Age and Correlation of the Deposits 



As these clays occur in a remote region, isolated from all other 

 known deposits of a similar kind, it i^ of interest to compare them 

 with clays of a similar character which are used in the clay working 

 industry at accessible localities. 



The northern Ontario fire-clays, as far as known, are all situated 

 on the low rather flat area of Palaeozoic rocks which lie between the 

 great central complex of pre-Cambrian rocks and Hudson bay. The 

 bottom of the fire-clay beds was not seen at any point where they were 

 examined as the basal beds lie below water level, and were not reached 

 by borings. 



The Palaeozoic rocks found nearest to the clays are sediments of 

 Upper Devonian age, and it is very likely that the fire-clay beds rest 

 directly on these. 



The lire-clays are all transported, fine-grained sediments and, as 

 the name implies, they are fairly pure materials, free from an excess 

 of fluxing impurities such as iron, lime, magnesia, and alkalies. Thin 



