1854.] HORNER IGNEOUS ROCKS IN CAWSAND BAY. 365 



branches from the great mass, and that the variety of aspect arises 

 from the diiferent conditions of their cooHng. The igneous rock 

 composing the dyke d appears to have been injected into several 

 cracks and fissures of the strata, and portions of the sandstone and 

 slate are enveloped by it ; without however causing any alteration in 

 their structure, and without any indication of metamorphic action. 

 It presents different aspects, as will be seen by the accompanying 

 specimens*. In one place it closely resembles the dyke A. 



Farther eastward, the sandstones and slates are heaved up on the 

 shore in a dome-shaped mass, the upper part of which has fallen in, 

 and the beds may be seen dipping to all points from N.N.E. round 

 by W. to the S., and a httle E. of S., presenting a miniature crater 

 of elevation. 



From this part of the coast to Redding Point, there is a succession 

 of the sandstones and slates, exhibiting great variety in the stratifi- 

 cation, there being frequent changes in the direction and dip, and 

 several instances of curvatures and arch-formed elevations. 



Having thus described the facts as I observed them, I will now 

 hazard some suggestions as to the theory of this association of igneous 

 and sedimentary rocks. That the porphyry is an igneous rock 

 which has issued in a molten state from the interior of the earth, 

 and as a submarine outburst, scarcely admits of a doubt. Such 

 rocks are either spread in a sheet over the sea-bottom and are after- 

 wards covered by sedimentary deposits, or they have been thrust into 

 openings between the beds of sedimentary rocks, or into rents that 

 cross their lines of stratification. The occurrence of a conglomerate 

 adjoining the porphyry on the eastern and western sides, so nearly 

 alike as to be almost identical, would not, of itself, contradict the 

 hypothesis of a sheet of molten rock poured out on the sea-bottom ; 

 because the outpouring and consolidation might occupy so short a 

 time that the same causes which collected the lower bed of conglome- 

 rate might have continued in operation. But while it is conceivable 

 and even probable that the melted matter might insinuate itself 

 among the pebbles and sand over which it flowed, it is not so con- 

 ceivable how it could be mixed with those that would be deposited over 

 it, as that surface would be cooled and consolidated by the water in 

 which it was poured out before any sand or gravel could be thrown 

 down upon it. The disturbed state of the stratified rocks on both 

 sides of the mass is also adverse to such an explanation. Judging 

 from that disturbance, and from the identity of mineral stnicture and 

 of the general dip of the strata on the east and west of the porphyry, 

 it seems to be most probable that the igneous rock was poured into 

 a vast irregular cavity parallel to the plane of stratification, and into 

 smaller lateral rents, both caused by the force which raised the sedi- 

 mentary rocks from their original horizontahty into their now highly- 

 inclined position. 



* Specimens Nos. 30 & 31. Specimen No. 32 is a detached and rounded 

 fragment included in Nos. 30 & 31. Specimen No. 33 is from a bed interstra- 

 tified with the sandstone and slate in the vicinity of the dyke 30 & 31. 



