1849, 1 extended the coal field from Iowa to the vicinity of the Kio 

 San Saba, expressing that opinion which I continue to think a true 

 one, by a general outline, without any claim to the exact correctness 

 of the boundary line, except near the thirty-fifth parallel of latitude, 

 where I have seen the exact limits. From the collections submitted 

 to me, I judged that the cretaceous rocks overlie and even conceal 

 from view the carboniferous rocks on both sides of the Red River, 

 near Preston, as shown on my map ; and if my limit is too far south by 

 one line or a fraction of a line, bringing the carboniferous into Collins 

 and Dallas counties, I am much obliged to Dr. Shumard for correcting 

 my mistake, but cannot see that my approximative limit is liable to 

 lead to serious errors^ as he thinks, on this account. A glance at the 

 Geognostische Karte von Texas, published in 1849, — the only one then 

 in existence, — in comparison with my map, will show the difficulties 

 to be surmounted, in the modification and enlargement, made by me, 

 especially as I had only been in the northern corner of the State, 

 near the River Canadian, a hundred miles distant from Red River, 

 and was obliged to make out the Triassic and Jurassic age of rocks, 

 then and at this time considered as cretaceous by Messrs. Shumard, 

 Meek, and Hall. 



The second memoir of Dr. B. F. Shumard, alluded to at the com- 

 mencement of this note, is entitled Observations upon the Cretaceous 

 Strata of Texas. (See Trans, of the Acad, of Science of St. Louis., 

 vol. I. p. 582. 1860.) 



In this memoir Dr. Shumard describes a theoretical section, show- 

 ing the order of succession of the different subdivisions of the Texan 

 Cretaceous System, so far as his observations go, and correct in the 

 main, he believes, although he admits that " further researches may 

 render some slight modifications necessary." The various groups of 

 strata, in regard to their statigraphical relations and fossils, were 

 " investigated very carefully," he says, and adds, " We have devoted 

 special attention to the inferior division of the system." Yet in the 

 description of the lower cretaceous, he admits that he is indebted to 

 his brother. Dr. G. G. Shumard, for a knowledge of it, and in the 

 description of its different subdivisions, he seldom gives the strata 

 which overlie or underlie them. 



The tabular view of the strata given by Dr. Shumard is here 

 given : — 



