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- 
ture, Emmons gives the thickness of this formation at the northern 
it probably 
“not 
6“ 
termination of the Helderberg range where he says 
forms the thickest mass of any other locality in the state”’ as 
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. 27, 1889) Mr Walcott gave a historical sketch of 
the term Hudson river group and added the results of recent in- 
1Geology of New York, pt 3, p. 61. 
*Geology of New York, pt 2, p. 119. 
3Manual of geology, ed. 4, p. 494. 
4Geology of New York, pt 4, p. 30. 
5Utica slate and related formations, Albany, 1879, p. 4. 
®6Contributions to the geology of the American continent, Salem, 1882, p. 41. 
