LOWER SILURIAN SYSTEM OF EASTERN MONTGOMERY CO. 429 



says, " alternates at its lower part with thin beds of dark colored 

 impure limestone and is connected by alternation and by organic 

 remains with the Trenton limestone. . . The Frankfort slate on 

 the contrary alternates with a peculiar sandstone to which Prof. 

 Eaton gave the name of rubblestone. The slate is wholly destitute 

 of calcareous particles and its great thickness in the first district, 

 though it diminishes going west and north, entitles it to a distinct 

 appelation."^ 



In the final report of Emmons the name " Lorraine shales " is 

 used as the designation of this terrane.^ In the Report on agricul- 

 ttire, Emmons gives the thickness of this formation at the northern 

 termination of the Helderberg range where he says " it probably 

 iorms the thickest mass of any other locality in the state " as " not 

 less than 700 feet " (p. 125). This is also the estimate given by 

 Dana.^ 



In Hall's final report it is stated that " where the strata are 

 undisturbed a well marked line of division usually separates this 

 group [Hudson river] from the Utica slate."^ Here the name 

 Hudson river group is used as is also the case in the final report 

 of Mather, the latter designation appearing in place of Hudson river 

 slate group (pt i, p. 367). 



C. D. Walcott says, *' In many instances it is difficult to indi- 

 cate the line of demarcation between the latter [Utica] formation 

 and the strata above or below, while in other localities the limits 

 of each formation are clearly defined."^ In an address before the 

 first Montreal meeting of the American association for the ad- 

 vancement of science, August 1857, Prof. James Hall said, " The 

 Hudson river group presents us on the one hand with a series of 

 soft shales becoming coarser and alternating with sandstones above, 

 and on the other with irregular masses of limestone and finally 

 immense masses of coarse sandstone or conglomerate with great 

 bands of shale. "^ In an address before the Geological society of 

 America (Dec. 2y, 1889) Mr Walcott gave a historical sketch of 

 the term Hudson river group and added the results of recent in- 



iQeology of New York, pt 3, p. 61. 



^Geology of New York, pt 2, p. U9. 



^Manual of geology, ed. 4, p. 494. 



*Geology of New York, pt 4, p. 30. 



^Utica slate and related formations, Albany, 1879, p. 4. 



•^Contributions to the geology of the American continent, Salem, 1882, p. 41. 



