140 Î>R. THOMAS STERRY HUNT ON THE 



iu Eurox^e and America, and were carried to an extreme in America. Mather, in his final 

 Report on the G-eology of the Southern District of New York, declared that " the Taconic 

 rocks are of the same age with those of the Champlaiu division, but modified by meta- 

 morphic agency and by the intrusion of plutonic rocks." They were, however, designated 

 by him as " imperfectly Metamorphic rocks," while the various crystalline schists of New 

 York and western New England, included by him in his group of proper Metamorphic 

 rocks, were declared to be the same series in a still more highly altered condition (§ 121). 

 Respecting these, he asserted that where the Taconic and Metamorphic rocks come together, 

 " no well-marked line of distinction can be drawn, as they pass into each other by in- 

 sensible shades of difference." Mather was disposed to admit, iu addition to these, an 

 older or so-called Primary series of crystalline rocks in the Highlands of the Hudson, but, 

 in the course of his Report, ended by declaring that the Primary limestones of southern 

 New York and northern New Jersey, with their associated granitic and hornbleudic rocks, 

 were nothing more than modifications of the members of the Champlain division. He had 

 been led to believe that the Primary limestones in question " can be easily traced through 

 all the changes from a fossiliferous to a crystalline white limestone, containing crystal- 

 lized minerals and plumbago." From the interstratification of these crystalline limestones, 

 supposed by him to be paleozoic, with gneissic and hornbleudic rocks, he was brought to 

 maintain the paleozoic age of these, and thus to doubt whether a part, at least, of what he 

 had called Primary gneiss was not also paleozoic. 



§ 1*74. Apart from the crystalline rocks of the Highland or South Mountain belt, whose 

 primary character was in part questioned by Mather, the great area of crystalline rocks 

 lying to the south and east of this range in New York, comprising those of "Westchester and 

 New York Counties, and embracing Manhattan Island, was by him included, with the adja- 

 cent rocks of western New England, in his Metamorphic series, and declared to be 

 " nothing more than the rocks of the Champlain division, modified greatly by metamorphic 

 agencies and by the intrusion of granitic and trappean aggregates." '* In this area of 

 southern New York he noticed hornbleudic rocks, gneiss, mica-schists and crystalline 

 limestones, besides granite, syenite and serpentine, the latter three being regarded by him 

 as intrusive rocks. 



§ ITS. The doctrine of the Metamorphic school of forty years since, as then resumed 

 and formulated by Mather, was briefly as follows : the different groups of crystalline 

 stratified rocks in south-eastern New York and western New England, (with the 

 doubtful exception of the gneissic belt which he had designated Primary), including the 

 Lower Taconic series, the series of micaceous gneisses and mica-schists, as well as the 

 massive granitoid and hornbleudic gneisses with their crystalline limestones, all belong to 

 one and the same geological period, and are contemporaneous in age with the paleozoic 

 rocks of the Champlain division of northern New York, from the Potsdam sandstone to 

 the Loraine shales, both inclusive. These various and unlike, though contiguous groups 

 of crystalline rocks, were, according to Mather, all produced from the same uncrystalline 

 Cambrian and Ordovician sediments, through a mysterious process of transformation, by 



'' For the details of tlie.se views see Mather's Geology of the Southern District of New York, 1S43, pasnm. 

 A summary of Mather's somewhat diffuse statements will be found in the author's volume on Azoic Rocks, Re- 

 port E of the Second Geological Survey of Pennsylvania, 1878, pp. 38-42. 



