explicit.] SOUTHERN AREA — RESUME. 141 



Besides the Tertiary groups, the sand-dunes of this area furnished a 

 subject of great interest. We had an excellent opportunity of studying 

 them and obtained some instructive data. Their behavior with refer- 

 ence to bodies of standing water is singular, and yet natural when 

 understood. More striking than the occurrence of the dunes is that of 

 the mud-springs. But few localities are knovvTi where they exist, and 

 never, to my knowledge, have they been found to exhibit the same type 

 as within our district. 



