92 On the 7Van.'jhion Rochs of the Calarwnu. 



He asserts, and with a great shew of reason on his side, that the 

 talcose and granular hmestones give a peculiar aspect to a great for- 

 mation composed of steatiiic, granular limestones, transition mica slate 

 and grcywacke, with primitive fragments j that porphyries aboiind- 

 hig in hornblende, but without metals and almost destitute of quartz, 



+ 



characterize another which is anterior to calcareous matter with or- 

 thoceratites ; that greywacke eminently distinguishes a third group 

 in which we find clay slate, limestone, porphyry and greenstone, and 

 that metalliferous porphyries, and sienites with zircon granites, are ' 

 the types of a fourth assemblage, which is posterior to transition clay 

 slate, and sometimes to limestone with orthoceratltes, whilst there is 

 a fifth composed of transition euphotide with jasper and serpentine. 

 Some of these groups, such as the porphyries and sienites, he also 

 says, appear to have an intimate relation to the trachytes, the most 

 ancient of volcanic rocks ; and others, the greywackes and porphy- 

 ries, as well as by the great accumulations of carbon, are also so 

 strongly connected with the secondary porphyries and d(?posites of 

 coal, that it Is often exceedingly difficult to separate porphyries, 

 amygdaloids and pyroxenic rocks from the red sandstone, with in- 

 terposed beds of greenstone and porphyry. Jameson, on the other 

 hand, places a red sandstone in the catalcsue of the transition fami- 

 lies of rocks. 



It is a very fivorite mode of getting over all these dijTiculties to 

 seek at once for the assistance of volcanic agency, and to make 

 every doubtful case, an igneous one. We shall, however, presently 

 see, that by mere accident, the strongest and the niosc difficult evi- 

 dence to overturn, has been produced on the shores of Lake Onta- 

 rio, w'hich may shake opinions so hastily formed. In a position 

 where die posldve nature of the igneous origin, or at least, the con- 

 version of rocky masses by volcanic agency or subterrene heat ap- 

 peared evident, even to the most inattentive observer, a momentary 

 inspection dissipated the illusion, and proved that, however plausible a 

 theory may appear, and however well it may be supported, it is still 

 possible for very simple and unexpected matter of fact entirely to 

 disperse It.* . 



* After a careful examination of the transition rocks of tlie Catarariui, at least of 

 the granitic varieties, many intellij^ent Iravellors and geolo^i.-ls have pronounc***! 

 them to be a-s clearly trap rock?! (in the volcanic sense) as those of Montreal, two 

 hundred miles to the castv.ard. If the facts, we shall state do not overset these as- 

 sertions, we shall still have another cause for repeating', how imperfect are all thi.- 

 data on which the modern systems of tiic blructure of the earth are founded. 



