LETTER TO THE SECRETARY. VII 



Massachusetts. Their importance and practical value are enhanced by their 

 presence in a country otherwise almost destitute of fuel. These Western 

 Coal- Measures render rail communication between opposite sides of the 

 continent not only practicable, but easy; they make possible the settlement 

 of an otherwise scarcely inhabitable country, and are invaluable in the prose- 

 cution of the mining and manufacturing industries of the Rocky Mountain 

 region. The plants which afTord this valuable combustible material merit 

 close study, no less from an economic than from a purely scientific point 

 of view. 



Other scientific deductions than those already presented are derived 

 from such investigations. To the study of the plants of the older Coal- 

 Measures we owe not only our knowledge of the vegetation of the several 

 geological epochs, but also our recognition of the diverse climatic conditions 

 which marked successive periods during the slow formation of the continent. 

 Until recently, the physical influences prevaiHng during the progressive 

 modification of the earth's surface from the earliest periods to the present 

 time have been considered in this connection only by the European palaeo- 

 botanists. Europe has seen the appearance of many works upon the fossil 

 plants of all her formations; but these records, however rich and interesting, 

 are incomplete without comparison with those of other continents. Deduc- 

 tions respecting the possible uniformity of the climatic conditions of any 

 one period over the whole hemisphere, or regarding the origin and distribu- 

 tion of plants, and the actual character of vegetable life, remain unreliable 

 and wholly unsatisfactory so long as they rest merely upon local observations. 

 The scientists of Europe, fully aware of this, have regarded the study of the 

 fossil botany of America as of the utmost importance, and have received 

 with evident satisfaction the first contributions to the knowledge of the 

 subject from investigations conducted in North America. A number of 

 memoirs have already appeared upon the Fossil Flora of the true Carbonife- 

 rous or Coal-Measures of the United States. The publication of Professor 

 Lesquereux's Cretaceous Flora of the Dakota Group, forming Vol. VI of this 

 series of Reports, awakened great interest in the whole subject, and incited 

 fruitfid discussions respecting the European formations of the same epoch. 

 The present volume, on the Tertiary Flora, opens a page of no less interest 

 and one still more important — one on which are traced the characters of a 



