MAGXfcSlAX SLATE* 



40 



Part of the Taconic Range from Stone Hill. 





^' "iornat toJ 



^--vr-^'^-^^^-'^^SS^^ 



§ 5. Magxesian slate. 



Produced in all periods. Different varieties. Characters. Restmblanee to slates of the Primary system. LiSho- 

 logical characters do not determine age: Instance the Cumberland coal-field. Milky quartz common in this 

 slate. .Absence of steatite, etc. in the Taconic range. Afotmtain ranges composed of this slate. Extent. 

 Soil and scenery. 



The almost endless diversity in rocks familiarly denominated slate, occasions much 

 perplexity to the student of geology. It is proper then to say in this place, for his special 

 benefit, that slate has been produced in all the periods -of the earth's history, or in all 

 formations ; that in all cases the original material must have been a mud highly charged 

 with clay, or alumine ; and that its composition varies greatly, from a pure clay or 

 alumina, to a silico-aluminous deposite, or an argillo-calcareous one. These ingredients 

 may exist in the slate in an endless diversity of proportions ; and in addition thereto, 

 magnesia enters into the composition of some varieties. These varieties are termed mag- 

 nesian slates, and may be usually known by their unctuous feel. The slate which succeeds 

 the Sparry limestone on the east possesses the latter character, and hence I have denomi- 

 nated it Magnesian slate. It is doubtful whether this rock is essentially different from many 

 portions of the Taconic slate ; still I believe that it is proper, upon the whole, to separate 

 them, as in their extremes they are quite different rocks. 



10* 



