92 On the Transition RocJis of the Cataraqui. 



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

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

 mation composed of steatiiic, gi'anular limestones, transition mica slate 

 and greywacke, with primitive fragments ; that porphyries abound- 

 ing 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 orthoceratites, 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 5 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 deposiies 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 catalogue of the transition fami- 

 lies of rocks. 



It is a very favorite mode of getting over all these difficulties 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 most difficult evi- 

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

 rio, which may shake opinions so hastily formed. In a position 

 where the positive 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 siill 

 possible for very simple and unexpected matter of fact entij-ely to 

 disperse it.* 



* After a careful examination of the transilion rocks of the Cataraqui, at least of 

 the granitic varieties, many intelligent travellers and geologists have pioiionnceil 

 them to be as clearly trap rocks (in the volcanic sense) as those of Montreal, two 

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

 sertions, we shall still have another cause for lepeating, how imperfect are all the 

 data on which the niodcrn systems of the structure of the earth are Ibunded. 



