MAGNESIAN SLATE. 
4 O 
Part of the Taconic Pange from Stone Hill. 
§ 5. Magnesian slate. 
Produced, in all periods. Different varieties. Characters. Resemblance to slates of the Primary system. Litho¬ 
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. Mountain 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 
alumine, 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* 
