IOWA ACADEMY OF SCIENCES. 37 



is of little importarce. But the prif-nnitic form of the sandstone is much more in- 

 teresting. The specimens gatliered were on or near the surface, and were not seen 

 in siiii; but from their great abundance it must be argued that they extend down- 

 wards for a considerable distance. It was first thought that possibly a dike rock 

 had once existed here, which had assumed the prismatic character, and that in some 

 way by surface decay it had left moulds into which the sand had been carried. But 

 a careful examination revealed no indication whatever of there ever having been a 

 dike here, although they are quite common in the surrounding country. The gran- 

 ite close by is older ' than the sandstone, and could not therefore have played any 

 part in the matter by metamorphosing the sandstone in any way. 

 ^ See Bull. No. 5. Mo, Geol. Sur. p. 12, et seq. 



THE TERTIARY SILICIFIED WOODS OF EASTERN ARKANSAS. 



BY R. ELLSWORTH CALL. 

 Read September 1891. 



(Published by permission of the State Geologist of Arkansas.) 

 The occurrence of silicified wood in the sands and gravels of the Tertiary of the 

 Lower Mississippi Valley has long been known. Aside, however, from the numer- 

 ous localities mentioned by Ililgard,* nearly all of which are in the State of Mis- 

 sissippi, little attention has been given it. Numerous geologists have spoken of 

 it or incidentally studied it in connection with other investigations, but hitherto no 

 attempt has been made to recognize the species and fix their taxonomic value, if, 

 indeed, they possess any such value. Among those who have investigated the 

 Orange Sands and other Tertiary deposits of the Mississippi Valley and who have 

 added to our information as to the occurrence of these fossils are Hilgard,f Pen- 

 rose,!: and Knowlton.§ 



The last named has made the only microscopic study of these fossils which is on 

 record. Since his investigations are based upon material which, for the most 

 part, was collected by the writer, it is thought that it will be useful to place on 

 record in this form, a more detailed statement of the conditions of the occurrence 

 •of the silicified woods, their peculiarities, their structural relations and their 

 stratigraphical position, in the hope that it may eventually prove to be of use in 

 correlating the deposits in which they are found. 



These fossil woods occur throughout the area covered by Tertiary sands and 

 gravels in the State of Arkansas. When in large masses they are apparently 

 rarely far removed ircm beds of Tertiary lignite, if in small masses or in small 



* Agriculture and Geology of Mississippi, 1860. pp. 20, 21, et seq. 



+ Agriculture and Geology of Mississippi. 1860. pp. 20, 21. ct seq. 



$ First Annual Report of the Geological Survey of Texas. 1889; "A Preliminary 

 Report on the Geology of the Gulf Tertiary of Texas from Red River to the Rio 

 Grande." By. R. A. F. Penrose. Jr.. pp. 1-101. 



§ See Annual Report of the Arkansas Geological Surrey for 1889, Vol. II. pp. 249-267, 

 Plates IX-XI. 



