Position of the Schistose Strata. 335 



these rocks in some localities contain but little plumbago. Tlie same 

 remark will apply to transition and secondary coal formations. For 

 example, the gneiss of Sturbridge, Mass. contains immense beds of 

 plumbago, — also the gneiss of the west side of Lake Champlain ; 

 though the gneiss of the same ranges contains little or none as we 

 proceed northerly or southerly. So the second graywacke of Penn- 

 sylvania contains beds of coal of vast extent ; while the same con- 

 tinuous stratum contains minute beds only in Catskill Mountain. 



That all the primitive schistose rocks are cotemporaneous, appears 

 from their extensive alternations and intermixtures. The following 

 series will be sufficient, at least to promote enquiry, if they do not 

 induce conviction. 



These alternations were carefully examined by Mr. Cortlandt 

 Van Rensselaer and myself, while on a geological tour from Man- 

 chester in Vermont, obliquely over to Boston, (a distance of about 

 one hundred and thirty miles,) in the month of June, 1829. 



1. Slaty granite — 2. Talcose slate — 3. Hornblende rock — 4. Mi- 

 ca-slate — 5. Hornblende rock — 6. Mica-slate, (transition argillite,) 

 — 7. Talcose slate — 8. Slaty granite — 9. Hornblende rock — 10. 

 Talcose slate — 11. Hornblende rock — 12. Mica-slate — 13. Slaty 

 granite — 14. Hornblende rock — 15. Talcose slate — 16. Hornblende 

 rock — 17. Talcose slate, (transition argillite) — IS. Talcose slate — 

 19. Slaty granite — 20. Talcose slate — 21. Hornblende rock, (tran- 

 sition argillite.) 



Dr. E. Emmons mentions a remarkable locality, in proof of the 

 cotemporaneous character of these primitive rocks, in the town of 

 Chester, Mass. Here one of the general ranges of hornblende rock 

 seems to be subdivided, so as to alternate with mica-slate more than 

 twenty times within the distance of half a mile. 



It is true that other rocks alternate at their approximating sides ; 

 but such extensive alternations are never observed among them. 

 When rocks alternate so extensively, we are bound to consider them 

 cotemporaneous ; consequently, " according to the sound logic" of 

 geology, each stratum is a constituent of the same formation. I be- 

 lieve the expression, same formation, is applied to all strata which 

 appear to have been produced by the same cotemporaneously oper- 

 ating causes. 



I hope to have the 2d part of the reports in readiness, together 

 with the map, for the April number of the Journal. 



Most respectfully yours, A. E, 



Rensselaer School, Troy, Nov. 2cl, 1829. 



