Petrographical Relations of ' Laurent ian Limestones, 29 



Smyth * says of these intrusions that the position of the 

 zone of extreme alteration, following all the irregularities 

 of the contact between the two formations, is sufficient 

 proof that it has been formed by the action of the one 

 on the other. This action, he says, can be explained in 

 no other way than as a case of contact metainorphism 

 resulting from the intrusion of the igneous rock into the 

 limestone. This conclusion is entirely supported by the 

 mineralogical composition of the contact zone, as the 

 species named, scapolite, hornblende, augite, titanite, etc., 

 are all recognized contact minerals, especially in lime- 

 stones. 



Furthermore, there seems no reason why metasomatism 

 should not have taken place in this occurrence as well as 

 it admittedly has in other regions. Many instances of 

 this kind could be cited. Among the notable ones are 

 the metamorphism; of mica schists by plutonic intrusives 

 in south-eastern New York, 2 and near Klausen 3 in. the 

 Tyrol, which have been noted by Rosenbusch 4 as present- 

 ing very similar phenomena; the contact of limestone 

 with monzonite at Predazzo. 5 and of the limestones of 

 Ramsberg in the Hartz 6 with granite, in both of which 

 cases broad zones of lime silicates have been formed ; and 

 perhaps one of the most striking instances of metamor- 

 phism is that of the Albany Granite ' in New Hampshire, 



, 1. loc. cit., p. 279. 



2. Williams, G. H., " The Contact Metamorphism Produced in the Adjoining Mica 

 Schists and Limestones. by the Massive Rocks of the ' Cortlandt Series,' near Peek- 

 s kill, N.Y.," Am. Jour. Sci., 1S88, Vol. XXXVI., pp. 254-268. On page 267 he describes 

 a dyke which is so narrow that the result of the whole action can be viewed at once 

 under the microscope, and there can thus be no doubt as to what has occurred. The 

 dyke cuts and alters limestone, and colorless pyroxene is one of the minerals produced 

 in the latter. Reference will again be made to this example. About a dyke in another 

 place, pyroxene, hornblende, sphene and quite abundant scapolite occur. 



3. Teller and von John, " Geologiseh-Petrographische Beitrage zur Kenntniss der 

 Dioritischen Gestene von Klausen in Sudtirol," Jahrb. der K.K. Geol. Reichsanstalt, 

 1882, Vol. XXXII., pp. 5S9-6S4. 



4. Rosenbusch, H., " Mikroskopische Physiographie der Massigen Gesteine," 3rd ed. 

 Stuttgart, 1896, p. 263. 



5. Lemherg, J., Zeit. d. d. geol. Ges., Vol. XXIV.. p. 234. 



6. Lossen, Ibid., p. 777. 



7. Hawes, G. VV ., Am. Jour. Sci., 1881, Vol. XXL, pp. 21-32. 



