BY G. D. OSBORNE. . 181 



base of the Glacial Stage there occurs in the central part of Portion 39, Parish 

 of Seaham, a characteristic volcanic breccia, consisting chiefly of uniform frag- 

 ments of dacitic ■ and rhj'olitic rocks, set in a matrix of volcanic dust with which 

 is associated a certain amount of secondary quartz. Fossil wood is abundant 

 in the main tuffs near Red Hill. 



An extremely detailed section of about 500 feet of the main tuft's, prepared 

 from the records of a diamond-drill bore, put down IJ miles to the north of 

 Seaham, has been given by Prof. David (David, 1904, pp. 111-112). There is 

 no need to reproduce the minute details of this section, except to point out th.at 

 the rocks passed through were entirely clastic, comprising tuffs of many kinds, 

 shales, tuffaceous sandstones, arkoses, etc. 



In places, particularly to the west of Paterson, the top layers of the main 

 tuffs have been altered into siliceous rocks by contact metamorphism from the 

 overlying toseanite. 



A summary of the stratigraphy of the Lower Portion of the Glacial Stage 

 is as follows: 



Thickness in Feet 



Basal conglomerates 100 



Volcanic Breccia of limited extent 30 



Red tuffs with pebbly bands . . . . 200 



Varves 40 



Fine tuffs 200 



Tufis with arkose bands 50 



Tuffs with pebbles 320 



Conglomerate 80 



Tufifaceous sandstones 700 



Conglomerate 80 



Tuffs with fine-grained strata carrying Rhacopteris fossils . 250 

 Tuf?s, with silicified upper surface 50 



Total Thickness 2100 



It has not been possible to say beyond all doubt whether the rocks con- 

 stituting the Paterson type of toseanite and dellenite are entirely extrusive or 

 intrusive. In some places there are features indicating extrusion, in others 

 evidence suggesting intrusion. For instance, tuffaceous phases occur, the frag- 

 mental material not having originated within the mass during crystallisation. 

 Also in the glacial beds overlying the toseanite in Dunn's Ck., there are numer- 

 ous boulders identical with the underlying igneous rock, and there is nothing in 

 the whole area examined to suggest that the present position of the basal glacial 

 beds was occupied by a former, now eroded, series, into which the toseanite was 

 injected. On the other hand one has to consider the following particulars. In 

 a number of exposures of the igneous rock one can see rounded pebbles firmly 

 embedded in it. It does not seem likely, in view of the fact that the mass of 

 toseanite is thick, that these pebbles represent loose material picked up by the 

 igneous rock when poured out as a lava, and transported to the surface by reason 

 of a difference in specific gravity of host and inclusion, or by other mechanical 

 means, although such must be regarded as possible. Also in places as, for 

 example, along the course of Dunn's Ck., there are fine-gi-ained string-s of 

 igneous material found among the glacial beds, just at their junction with the 

 toseanite, and these seem to originate from the toseanite, although this point is 

 not clear. If these strings are continuous with the main igneous mass, it is 

 difficult to explain their present positions, except as being due to forces of in- 

 trusion. In the case of a unit being a sill in one place and a flow in another. 



