152 APPENDIX D. GEOLOGY. 



iferous." It continued, however, to the 30tb, or to Fort Washita, where 

 he says, " I observed in it a large number of the fossils characteristic of 

 the cretaceous period." Probably he refers to two kinds of limestone, 

 and not improbably the limestone and sandstone first noticed belong to 

 the carboniferous strata already noticed. Among the specimens I also 

 find parts of two species of ammonite ; one quite large, but quite char- 

 acteristic of the cretaceous strata, and resembling some good specimens 

 in the collection of the American Board of Foreign Missions, obtained 

 by their missionaries in the Choctaw country. I cannot doubt that 

 these strata are largely developed in that vicinity. Indeed, that region 

 has already been colored as of the cretaceous age upon our geological 

 maps. 1 have, therefore, marked a strip of cretaceous rocks between 

 Forts Belknap and Washita. These are, in truth, the predominant 

 strata in Alabama, Mississippi, and Texas, and I need not go into details 

 respecting them. 



Dr. Shumard frequently speaks of a surface formation under the 

 name of drift, consisting of boulders of all the rocks ■ described above, 

 and some others, such as mica slate and labradorite. But I doubt 

 whether this formation be the same which we denominate drift in New 

 England — the joint result of water and ice ; for no example has as yet 

 been found of drift agency as far south as Texas, by several degrees. 

 Yet there is evidence of a southerly movement among the smaller 

 rolled detritus almost to the Gulf of Mexico, such as water alone could 

 produce, seeming to be the result of the same current, destitute of ice, 

 that produced the coarse unstratified and unsorted drift of Canada and 

 New England. But among the specimens in my hands are several of 

 silicified wood, and all of them, I believe, are mentioned in Dr. Shu- 

 mard's notes as occurring in drift; although in your letter of December 

 5, 1852, you speak of masses from fifty to one hundred pounds in 

 weight in the gypsum formation. You may mean in its upper part ; * 

 if so, there may be no discrepancy between the two statements ; and I 

 have been led to suspect that what Dr. Shumard calls drift may be 

 only a newer portion of the tertiary strata, although, as already re- 

 marked, silicified wood is found in almost all the fossiliferous formations. 

 All the specimens sent by you, however, with one exception, are dicoty- 

 ledonous. They resemble not a little the fossil-wood from Antigua, and 

 the desert near Cairo, in Egypt ; both of which deposites are tertiary. 

 One specimen is a beautiful example of a monocotyledon, a cross see- 

 the fossil-wood referred to in Captain Marcy's letter was found upon the 

 upper surface of the formation. 



