148 ROYAL SOCIETY OF CANADA 



acter the strata are quite ditferent from those of the typical Black Eiver 

 of the lower Ottawa. These lieds extend along the stream to L'Kveille 

 Rapids, a distance of about three miles, and the elevation of this point is 

 480 feet above sea. Interestini;,- outliers also occur on some of the islands 

 in Lake Nipissing, at an elevation of 642 feet. These are also of Black 

 River age, but like those last mentioned the strata diflfer in aspect fi-om 

 those of the lower Ottawa, though the contained fossils are similar. 



^^he formations recognized in all these PaUeozoic outliers, are for the 

 most part, highly fossiliferous, with the exception of the Potsdam sand- 

 stone. \n this, as developed in the lower Ottawa basin, the principal 

 traces of organic remains are seen in the peculiar markings known as 

 Scolithas. which, on weathered surfaces, present the form of nearly 

 cylindrical holes from the twentieth to the eighth of one inch in diameter. 

 Some of the strata are thickly studded with these markings which pene- 

 trate the rock to a depth of several inches, sometimes in a direct course 

 but frequently curved, and often ii*regularly contorted. The origin of 

 these is, as yet, doubtful. Other peculiar markings found on the surfaces 

 of certain beds of the sandstone have apparently been caused by the 

 passage of some crustacean across them, of which, however, no trace has 

 yet been found in the rock itself. These have received the name of 

 Protichnites. As we approach the transition beds between the sandstones 

 and the calcareous members of the Calciferous, however, several well 

 deriiu.'d forms of brachiopods, gasteropods and cephalopods occur, among 

 which species of Linyula and Ophileta are recognized. These are well 

 seen on the southern margin of the main Ottawa basin at Beverly, in the 

 township of Bastard, not far from the head of the chain of the Rideau 

 lakes, and these fossils may be held to mark the lowest well defined forms 

 of organic life yet found in the Cambro-Silurian system of the Ottawa 

 basin and that of the St. Lawrence basin adjacent. 



While the strata in all the areas described are for the most part 

 neai'ly horizontal, indications of faults are clearly visible at a number of 

 points and tend to render uncertain the calculations made to determine 

 the thickness of the several geological divisions. Several of these can be 

 well seen about the city of Ottawa and in the country to the west 

 between that place and Arnprior. Along the lower Ottawa also, al)Out 

 Ilawkesbury and L'Orignal, several bi'eaks can be observed which atfect 

 the strata of the Chazy and Black River formations. 



The presence of intrusive masses is also clearly seen at several points, 

 among which may be mentioned the Potsdam area of Nepean, near the 

 line of the township of March, where dykes cut the underlying Lau- 

 rentian as well as the overlying Potsdam sandstone. These are particu- 

 larly well seen in the cuttings of tlie Ottawa and Parry Sound railway ; 

 while further west near Portage du Fort the Calciferous beds are also 

 similarlv attected. 



