



LETTER TO THE SECRETARY. 



Office of the United States Geological 



Survey of the Territories, 



Washington, D. C, June 1, 1876. 



Sir: 1 have the honor to present, for your approval and for publication, 

 the accompanying memoir on the "Invertebrate Cretaceous and Tertiary 

 Fossils of the Upper Missouri Country"' by F. B. Meek, and to commend it 

 to the attention of the Department as one of the most important contribu- 

 tions ever made to the science of palaeontology in any portion of the world. 



To the geologist who may hereafter study the various groups of sedi- 

 mentary strata over our widely-extended western domain, this volume will 

 prove indispensable. The different divisions or groups of the Cretaceous 

 and Tertiary ages, especially of the former, were originally established by 

 the invertebrate remains herein described, and it therefore forms the basis 

 of our knowledge of two of the most important formations in the West. As 

 one of the series of volumes, in which are included • those of Leidy, Cope, 

 and Lcsquereux, it forms a most valuable contribution toward the solution 

 of one of the difficult problems in western geology, the relations of the 

 Lignitic group to the well-defined Cretaceous immediately beneath it. The 

 enormous labor which the author has expended on the discussion of the 

 genera and species, together with the synonymy, will be apparent to the 

 palaeontologist at a glance. 



The accumulation of the materials which compose this volume was 

 commenced in the spring of 1854, and the greater number of the new species 

 of fossils were discovered by the writer of this letter during that and the 

 succeeding year. From 1856 to 1858, he was attached to the Exploring 

 Expedition to the Northwest, as geologist, under the command of General 

 G. K. Warren, United States Engineers; and in 1859 and 1860 he was 



