Frazer.j ^'^ [April 21, 1870. 



these portions of the map too deeply to allow of the delineation of the other 

 portions. The unnatural etfect is produced, of a map construc'.ed on two 

 ditlerent hypsomelrical scales. 



The distrihniion of rock, sand, slime, etc. along those sea bottoms which 

 have been best observed (as for instance in the British Channel and along 

 the routes of various deep sea sounding lines) is very interesting. 



The great distance to which fluviatile sediments are carried and the sepa- 

 rate although adjoining areas which the susi)ended matters of two widely 

 separated river systems will occupy is strikingly shown in the distinct 

 bells of St. Lawrence and Mississippi sand which overlap for 500 miles 

 along our coast without commingling. 



For his contribution to our knowledge of our own coasts M. Delcsse de- 

 serves the hearty thanks of every student of American physical geography 

 and geology. 



Mr. Lesley added his testimony to the sjreat value of the 



work of M. Del esse, of which Prof. Frazer had spoken : 



He hoped that the Lithologie du Fond des Mers would he translated into 

 English, and the magnificent maps accompanying it republished for the use 

 of American geologists. If only the one map of the American continent and 

 its enclosing water-beds were published, showing by colors the different 

 sediments which issue from our rivers, and are distributed by tidal currents 

 along our coasts, it would be a most valuable addition to our handbooks of 

 geology. Man}' of the problems of erosion and sedimentation in Mesozoic 

 and Kainozoic times, are plainly helped to solution bj' this map. 



One of the most striking features is the contrast between the sediment in 

 front of the coast from Maine to Alabama, and that of the sediment filling 

 the St. Lawrence Gulf, and tapering southwards to a point ojipcsite Nor- 

 folk. The former sediment fills the in-shore angle of the Gulf of Mexico, 

 in front of Pensacola ; the latter is repeated as an outside belt, stretching 

 from the mouth of the Mississippi to a point in front of Havana. 



It is easy to see the cause of the difference. The inside sediment descends 

 the rivers whicii drain the siliceous and feldspathic mountains of New Eng- 

 land, New York and Pennsylvania, Virginia, the Carolinas and Georgia, 

 composed of Azoic and Palisozoic formations. The outside sediment de- 

 scends the St. Lawrence and the Mississipju, and represents the drainage 

 of the argillaceous and calcareous interior of the continent, composed of the 

 Sub-carboniferous limestone formations east of the Mississippi, and of 

 the broad stretches of Cretaceous and Tertiary rocks between the Missis- 



sipi)i and the Kticky Mountains. 



The map suggests plainly the cause of the difference between the consti- 

 futional features of the eastern and western Cretaceous and the eastern and 

 western Tertiaries. 



A thousand details of this nature will repay the student of the map, to 

 construct wbich must have tasked the zeal, as well as the knowledge, of 

 tlie distinguished French geologis', its autlior, to tlie utmost. 



M. Delcsse is naturally desirous that tliis mapsliould be known to Ameri- 

 can geologists, and to receive from them, directly or indinctly, such criti- 

 cisms of it as will enable him to improve it in future editions. 



