Smith.] ^14 [Oct. 2, 



Preface. 



The Coal Measures cover an area of 14,700 square miles in the State 

 of Arkansas. The greater part of this area lies in the geosyncline of 

 the Arkansas Valley. Tlie total thickness of the sediments in this 

 geosyncline is enormous — 24,000 feet. These conditions, taken in con- 

 nection with the occurrence in these sediments of both land plants 

 (coal beds) and of marine fossils seem to show that the beds were de- 

 posited upon a subsiding (for the most part) floor, and that the land 

 stood near the sea level, below which it occasionally sank. 



The marine fossils from the Coal Measures area, so far as they were 

 collected by the Geological Survey of Arkansas, are listed and described 

 in the following paper kindly prepared at my request by Dr. J. P. 

 Smith, of Stanford University. It is volunteer work done origin- 

 ally for the State Survej^ and was to have been published in a volume 

 upon the paleontologj' of Arkansas. Upon the abolition of the Survey 

 by the Legislature in 1893 several volumes of reports were left unpub- 

 lished, and among them one on the paleontology of the State. 



John C. Branner, 



Late State Geologist of Arkansas. 

 Stanford University, California, July 10, 1896. 



Introduction. 



Marine fossils afford the best means of correlating strata of different 

 regions, but in the Coal Measures they are usually rare, and therefore of 

 especial interest and \^alue when found. 



Of all the Paleozoic systems the Carboniferous is most subject to 

 facies variations, which make it difficult and often impossible to recog- 

 nize with certainty the minor subdivisions at any great distance from 

 the place where they were first established. This is true even of the 

 Mississippian formation, whose limestones were deposited under com- 

 paratively uniform conditions, so that one would expect the fauual rela- 

 tions to be the same over the whole area where the Mississippian facies 

 prevails. But the American Coal Measures were formed under condi- 

 tions not favorable to uniformitj^ either of rock character or of life, 

 hence the correlation of tliese strata becomes more difficult. And in 

 these geologists have been more prone to rely on lithologic charac- 

 ters and unaided stratigraphy. Such correlations have only a local 

 value, and cannot be extended over any wide scope of territory. For 

 this reason no divisions of the Coal Measures into zones has every been 

 carried out, nor can it be done, in the present state of our knowledge. 



Previous to the collections made by the Geological Survey of Arkan- 

 sas, marine fossils were known from but a single locality in the Coal 

 Measures of Arkansas. Dr. David Dale Owen, in his Geological 

 Eeco?inoissance of Arkansas, Yo]. i, p. 68, says: "Three miles north- 



