218 ASHLEY — GEOLOGY OF ARKANSAS. [May 13, 



these beds as the top of the Lower Silurian or the bottom of the 

 Coal Measures is simply that the novaculites, as considerable beds, 

 end abruptly with this stratum, and because this bed is a conglom- 

 erate. It will be seen that there are some thin and unimportant 

 beds of novaculite above this horizon, but they are no more to be 

 compared with the novaculites below it than are the coal beds of 

 the Devonian to be compared with those of the Carboniferous. 



So far as I can judge from my own observations there is no 

 marked unconformity between the Lower Silurian rocks and the 

 Lower Coal Measures rocks, and that in spite of the fact that there 

 are no Devonian rocks known to be such in this part of the State. 

 The conglomerate, however, suggests the possibility of such an 

 unconformity, and it is quite possible that the disturbed condition 

 of the rocks has caused such a gap to be overlooked. 



Mention is made at several places of a stratum of supposed 

 igneous rocks interbedded with the sedimentary ones, and assumed 

 by Dr. Ashley to be everywhere at the same horizon. There is 

 some doubt in my mind as to whether this bed is everywhere the 

 same, and also as to whether it is really igneous. There is no 

 doubt but that the bed discovered by Dr. J. P. Smith in 5 south, 

 32 west, section i, is a tuff, but at other places the rock is so 

 changed by decomposition that it is not possible to say with cer- 

 tainty what the original materials were. It is also suggested by the 

 author that these beds are to be correlated with similar rocks sup- 

 posed to be volcanic tuffs and found about Cushman, Independence 

 county, in the northern part of the State. But this north Arkansas 

 bed turns out to be a phosphate deposit, and a chemical analysis of 

 one of Dr. Ashley's specimens from southwest Arkansas shows it to 

 contain an equivalent of nine per cent, of calcium phosphate.^ 



To the little proof here given of the age of these Lower Coal 

 Measures rocks should be added that I have found Calamites in 

 this series on the west bank of the Ouachita river in 5 south, 18 

 west, section 32. Attention should also be directed to the notes of 

 Prof. C. S. Prosser on the " Lower Carboniferous Plants from the 

 Ouachita Uplift," published in the Novaculite Report of the Arkan- 

 sas Survey (Vol. iii, 1890, pp. 423, 424). Prof. Prosser's notes 

 are upon fossils found north of the region described in the present 



See " The Phosphate Deposits of Arkansas," by John C. Branner, Trans. 

 Amer. Inst. Mining Engineers, September, 1896. 



