FI.CKTZ TRAP FOUMATIONS. 209 



Stances, been laid hare by the action of water, which has 

 worn away the superincumbent stratum, as is the case on 

 tlic Vermihon llivcr, a Ijrancii ol' the I'latte wiiich rises in 

 the plains at a considerable distance to the east from the 

 peak. This argillaceous or grey sandstone is the uj)per- 

 most of those horizontally stratilied rocks which are seen in 

 this region, jwssessing within tiiemselvcs convincing evidence 

 of their having been formed by deposition from the waters 

 of the ocean. 



Another family of rocks of recent, but doubtful, origin, 

 which are usually found resting on the sandstone last men- 

 tior)ed, remains to be considered. These are rocks of ba- 

 saltic or tiappean conformation, by some geologists deno- 

 minated su|)erincumbent rocks, and by many supposed to 

 Ixj of volcanic origin. 



They present a striking contrast by their dark colour, and 

 the vastness and irregularity of their masses, to the smooth, 

 light, and fissile sandstone on which they rest. In their tex- 

 ture and external conformation they often make a nearer 

 approach to the piimitive rocks than to those denominated 

 secondary among which they occur. Their appearance and 

 position are such as to lead almost involuntarily those least 

 attached <o visionary theories into speculations concerning 

 their oiigin. Sometimes they are observed compact and ap- 

 parently homogenous in their composition, presenting a crys- 

 talline rather than a stratiform appearance, and in many parti- 

 culars of structure, form, hardness, colour, ^c. seeming close- 

 lyalliedtothe rocks of primitive formation. In other instances, 

 black and scmivitrilied substances are seen scattered al)out 

 the plains, or heaped in conic niasses, but never ap|)roacliing 

 in character the rocks on which they rest. Most of the rocks 

 of this sort which were observed, arc found in the country 

 about the sources of the Canadian FJiver. Amons; them may 

 be distimjuished two kinds referable to two divisions of the 

 class called by Werner superincumbent rocks, viz. green- 

 stone and amygdaloid. 



i. Greenstone. nninstoin. JFrrn. Roche ami)hibo- 



