330 MESOZOIC FLORAS OF UNITED STATES. 



of the Mesozoic sea when, it bordered upon the Carboniferous continent. The lowest 

 marine fauna of this division is seen in Parker County and careful study of the same 

 may prove Jurassic affinities. 



Mr. Hill extended his observations into Arkansas and Indian Ter- 

 ritory, cooperating with the State Survey of Arkansas and contributing 

 to its reports. He found that the basal sands extended into that State, 

 and he traced them as far as he could find them. In a short prelimi- 

 nary paper"^ published in Science, at the beginning of 1888, he first named 

 the Trinity formation. He briefly describes and locates it in both 

 Texas and Arkansas, and says: "In Texas I found what are at present 

 supposed to be dinosaurian remains, and occasional vegetal remains are 

 met with," and adds: "To the continuous formation the name of 'Trin- 

 ity' is applied, from the rivers of that name which arise in it. This 

 includes the strata which I termed 'Dinosaur sands' in my Texas section." 



It was, however, principally in his extended paper in the Annual 

 Report of the Geological Survey of Arkansas for 1888 * that he fully set 

 forth the relations of these beds. Thej^ are here called the Trinity 

 division of the Comanche series. He gives them a thickness of over 

 400 feet and says that in Texas "innumerable contacts between this 

 formation and the base of the Comanche series have been seen by the 

 writer and prove that it is below and older than our oldest Cretaceous 

 (p. 124). * * * Ji^ Texas and Indian Territory the westernmost 

 beds are beneath the Neocomian. Reviewing the stratigraphic evidence 

 afforded by the Trinit,y formation it seems to be clearly older than 

 any Cretaceous rocks hitherto described in this country, a fact which 

 is verified by the paleontology, as shown in the next chapter" (p. 125). 



The paleontology given is almost exclusively molluscan, the sup- 

 posed vertebrate remains not having been as yet determined, and the 

 plant remains being for the most part indeterminable, notwithstanding 

 his reference to them as "abundant." They were referred to Dr. F. H. 

 Knowlton, who reported briefly upon them in a letter which Mr. Hill 

 publishes on page 152. The problematical form to which Doctor 

 Knowlton refers was subsequently described (see p. 340). 



" The Trinity formation of Arkansas, Indian Territory, and Texas, by Robert T.Hill: Science, Vol. XI, 

 January 13, 1888, p. 21. 



l> Neozoic geology of southwestern Arkansas, by Robert T. Hill, assistant geologist: Ann.Rep.Geol.Surv 

 Arkansas for 1888, Vol. II, 1888, pp. 1-354. See pp. 116-152. 



