1869.] WALLBEIDGE CANADA WEST. 265 



the thick-bedded limestone are found in the Laurentian area of 

 Madoc, at a considerable distance from the main mass. In a lec- 

 ture delivered at Madoc in 1866, 1 called attention to these outlying 

 patches. One of them occurs about a mile south of the Eichardson 

 gold-mine, and the other at a distance of about 2 miles S.E. of 

 the former mass. The N. and N.E. sides of these outliers present 

 prominent escarpments, whilst the other sides have a gentle slope. 

 Other smaller outliers of limestone are scattered over the Laurentian 

 area ; and all are of interest as attesting the extensive denudation 

 which the country has suffered. 



At the base of the Trenton group there is found in certain locali- 

 ties of the North Eiding a thin band of grey limestone, having so 

 extremely fine a texture as to render it well adapted for use as a 

 lithographic stone. 



In the township of Hungerford* the Trenton limestone is occa- 

 sionally underlain by an unfossiliferous calcareous sandstone, sup- 

 posed to represent the Calciferous Sand-rock and Potsdam Sandstone, 

 which form the base of the Lower Silurian formation. 



4. Laurentian. — The Lower Silurian beds usually rest uncon- 

 formably upon a very irregular surface formed by the denuded edges 

 of a large group of highly inclined strata of metamorphic rocks, 

 which have been referred provisionally to the Lower Laurentian 

 formation. These rocks are exposed over a large portion of the 

 North Eiding, and consist of a very diversified series of micaceous, 

 hornblendic, and chloritic schists, interstratified with beds of gra- 

 nular and crystalline limestone, and penetrated by bosses of syenitic 

 and gneissoid rocks. Bands of conglomerate occiu* locally, and con- 

 sist of quartzose, felspathic, and calcareous pebbles, imbedded in a 

 matrix of micaceous schist or of dolomitic limestone. Most of the 

 stratified Laurentian rocks exhibit evidence of having been highly 

 disturbed, the dip being extremely irregular, and often at a very 

 high angle. An apparent inversion of the rocks may be seen in the 

 adjoining townships of Tudor and Madoc. Traces of an organic 

 structure referred to Eozoon Canadense have been detected by the 

 Geological Survey of Canada in the limestones of Madoc and Tudor; 

 but it is supposed that these rocks may be placed on a higher 

 horizon than the Eozoonal limestones of Grenville. Indeed Sir 

 William Logan admits that the stratigraphical position of the crys- 

 talline rocks of Hastings is by no means satisfactorily determined ; 

 but he adds that " it would be premature to remove them from the 

 horizon in which they have been provisionally placed." 



In addition to the extensive development of these so-called Lau- 

 rentian rocks in the northern townisliips, domes of similar syenitic 

 and gneissoid rocks are exposed in several parts of the Trenton- 

 Limestone area to the south, Avhere the overlying limestone has been 

 planed down or removed by denudation. 



It has been suggested that certain labradorite rocks forming a 

 range in the township of Tudor, known locally as the " Hole in the 

 Wall," may be regarded as outlying masses of the Labrador or 

 Upper Laurentian series. 



