220 Dana and Chambers on Ancient Sea-Margins. 



MacCulloch,* and carried out with still more minuteness of 

 detail. 



1. The heights of the terraces above the bottom of the river- 

 valley on both sides should be measured by careful levelling, 

 and sections should be thus made through the whole course 

 of the stream, from its mouth to its head, at as many places 

 as practicable. 



2. The height of the river above the sea, should also be ob- 

 tained for each place where a section is thus made. 



3. The horizontality or slope of the terrace-plains along 

 the valley should be determined ; and to this end, the length 

 of any breaks in a line of terraces, met with on the ascent of 

 a stream, should be noted, and the physical features where 

 such breaks occur, in order to understand the causes of them ; 

 also the nature of the river's bottom, upon which fact it often 

 depends, whether the terraces may or may not correspond in 

 slope with the existing slope of the stream, and also what 

 may be their height in difterent places. 



4. The relation should be ascertained, if there be any, be- 

 tween the heights of terraces on the smaller tributaries and 

 those of the main stream, or between the stream where the 

 descent is rapid, and where it is nearly horizontal ; also be- 

 tween small and large streams in the same vicinity. 



5. The character of the deposits, whether alluvial, lacus- 

 trine, or of beach or sea-coast origin, applying the tests 

 mentioned, should be matters of thorough investigation. As- 

 suredly, if no marine relics or indications are found along a 

 river's terraces, for one or two hundred miles, it would be 

 defying all geological principles to assert that such deposits 

 were marine. 



A river-valley should thus be surveyed from its mouth to 

 the heads of all its tributaries. The Connecticut in our own 

 country affords a most interesting region for investigation ; 

 for the terraces are on a magnificent scale, and may be traced, 

 as the writer has seen, even among the White Mountains. 

 One river thus studied, will be a standard of comparison ; and 



* See Geol. Trans., vol. iv., Pl. 21. 



