Notices of Memoirs — Dr. T. S. Hunt on the Appalachians, 77 



tains of Vermont ; and (3), The White Mountains of New Hamp- 

 shire. 



(1), The Adirondack series, to which the name of the Laurentian 

 system has been given, is composed chiefly of granitic gneisses, 

 which are frequently hornblendic, but seldom or never micaceous. It 

 contains no argillites, which are found in the other two series. The 

 quartzites, and the pyroxene and hornblendic rocks, associated with 

 great formations of crystalline limestone, with graphite, and immense 

 beds of magnetic iron ore, give a peculiar character to portions of the 

 Laurentian system. 



(2). The Green Mountain or Huronian series consists largely of a 

 fine-grained petrosilex or eurite ; true gneiss, which is ordinarily 

 more micaceous than the typical Laurentian gneiss, also occurs. 

 Massive stratified diorites, and epidotic and chloritic rocks, often 

 more or less schistose, with steatite, dark coloured serpentines and 

 ferriferous dolomites and magnesites, also characterize this gneissic 

 series. These are intimately associated with beds of iron ore, gene- 

 rally a slaty haematite, but occasionally magnetite. Chrome, titanium, 

 nickel, copper, antimony, and gold are frequently met with in this 

 series. The gneisses often pass into schistose micaceous quartzites, 

 and the argillites, which abound, frequently assume a soft, unctuous 

 character, which has acquired for them the name of talcose or 

 nacreous slates, though analysis shows them not to be magnesian, 

 but to consist essentially of a hydrous micaceous mineral. They are 

 sometimes black and graphitic. 



(3). The White Mountain series is characterized by the predomi- 

 nance of well-defined mica-schists, interstratified with micaceous 

 gneisses. There are also beds of micaceous quartzite. Hornblendic 

 gneisses and schists occur, which pass occasionally into beds of dark 

 hornblende-rock, sometimes holding garnets. Here and there beds 

 of crystalline limestone are also found, and sometimes accompanied 

 by pyroxene, garnet, idocrase, sphene, and graphite. They are 

 intimately associated with highly micaceous schists containing stauro- 

 lite, andalusite, cyanite, and garnet. To this third series belong the 

 concretionary granitic veins abounding in beryl, tourmaline, and 

 lepidolite, and occasionally containing tinstone and columbite. 



Dr. Hunt traces out the geographical distribution of these three 

 groujDs, and discusses the opinions of different observers in regard to 

 their relative ages. His own conclusion is that the whole of the 

 crystalline schists of eastern North America are Pre-Cambrian in age. 



Eeferring to the evidences of similar rocks in other countries, he 

 states his opinion that the crystalline rocks of Anglesea and the 

 adjacent part of Caernarvon, mapped as Cambrian by the Geological 

 Survey of England, are probably of Pre-Cambrian age, a view which 

 he mentions is supported by the opinions of Sedgwick and Phillips. 



These rocks appear to him to be identical with the rocks of the 

 Green Mountain series. 



In the Highlands of Scotland there exists a great volume of fine- 

 grained, thin-bedded mica-schists, with andalusite, staurolite, and 

 cyanite, which are met with in Argyleshire, Aberdeenshire, Banff- 



