4 4 FRA NK DA WSON A DA MS 



somewhat softened and pulled out into more or less elongated 

 forms, appearing as dark streaks in the granite. The shale has 

 been recrystallized, as in the case of every hornstone, the phe- 

 nomenon being, of course, more pronounced in the separated 

 fragments which are completely enveloped in the granite magma. 

 The " lit-par-lit" injection is a not unusual phenomenon of con- 

 tact in all igneous intrusions, and merely produces a mechanical 

 admixture of granite with shale along the immediate contact of 

 the intrusion without in any way necessarily altering the com- 

 position of either rock, or producing anything which is not 

 manifestly a mixture of two distinct rocks. The appearance of 

 feldspar in the altered shale : — its " feldspathisation par imbibi- 

 tion" — does not necessarily indicate any addition of material. 

 If there were not alkalies in the shale, the appearance of feld- 

 spar in the altered rock would be an evidence of the addition of 

 these elements. But, as the analysis of shales from all parts of 

 the world show, alkalies are almost invariably present, amount- 

 ing on an average to about 4.75 per cent. This would, in the 

 case of a thoroughly recrystallized rock, afford the material for 

 as much as 25 or 30 per cent, of feldspar, and it would seem 

 that there is seldom more, or in fact as much as this, present in 

 the Leptynolite. 



Gneissic rocks of a peculiar type found continually associated 

 with the Laurentian limestones of Canada, and which have pre- 

 cisely the character of the more altered forms of these Leptyno- 

 lites, when analyzed have been found, in many cases, notwith- 

 standing their content in feldspar, to have a chemical compo- 

 sition identical with that of ordinary roofing slate, being in fact 

 nothing more than shales which are completely recrystallized. 

 On the other hand, thin sections of the most altered leptynolite 

 from Pont de Kerkabanac contain more feldspar than would be 

 expected in an altered shale. 



While, then, it is impossible to assert that there has been no 

 addition of material to the altered shale, no evidence seems to 

 have been brought forward that there has been such addition, or 

 that these occurrences differ from the ordinary type of contact 



