HANDBOOK FOR THE DEPARTMENT OF GEOLOGY. 543 



Phospbatic sandstones, as the name indicates, are arenaceous rocks. 

 Those from the Carolinas are dredged up in the form of rounded nodular 

 masses from river bottoms, and consist of siliceous and calcareous sand 

 with imbedded bones, fossil teeth of sharks, and other animal remains. 

 These rocks are often of value as fertilizers, and a more complete dis- 

 play is to be found in the systematic collections of the South West 

 Court. 



Bone breccia consists mainly of fragmentary bones of living or ex- 

 tinct mammals. These are often cemented compactly by stalagmatic 

 deposits. 



II — Aeolian rocks. 



This group comprises a small and comparatively insignificant class 

 of rocks formed from materials drifted by the winds, and more or less 

 compacted into rock masses. They are, as a rule, of a loose and friable 

 texture and of a fragmeutal nature. Many of the volcanic fragmental 

 rocks (tuffs) are grouped here, their materials having been thrown from 

 the volcanic vent in small fragments and drifted long distances by wind 

 prior to falling upon the surface of the ground or into the water for 

 their final consolidation. 



The group will be more fully described under the head of processes of 

 rock formation and the transporting power of atmospheric currents. The 

 volcauic members of the series are represented by the fine pumiceous 

 dust drifted from Iceland to the coast of Norway. (Specimen No. 

 35800); by the beautifully fine white dust from Orleans, Nebraska, 

 (37023); Gallatin Valley, Montana, (38588); Lake Lahontan, California, 

 (37208), and other sources in Montana, Colorado and Nevada. 



In specimen No. 20255 we have an example of the fine calcareous 

 sand formed on the beaches of Bermuda and drifted inland by the 

 winds, often forming high hills or dunes which overwhelm vegetation 

 and dwellings. Specimen "No. 25197 shows the same sand consolidated 

 by the solvent action of percolating water. (See collection illustrating 

 the geology of Bermuda, and also the transporting power of atmos- 

 pheric cm rents.) 



Ill— Metamorphic rocks. 



Under this head is grouped a large series of rocks which have been 

 changed from their original condition through dynamic and chemical 

 agencies, and which may have been in part aqueous and in part of 

 eruptive origin. Were it possible it would have been better to classify 

 the rocks of this group uuder those of the other groups from which 

 they were derived by this process of change, or metamorphism as it is 

 called. In only too many cases, however, this change has been so com- 

 plete as to quite obliterate all such traces of the original character as 

 would lead to safe and satisfactory conclusions. In some instances 

 it is nevertheless possible to trace the various stages of these chauges 

 through less and Je§s altered forms to the origiual fragmental or 



