24 REPORT OF NATIONAL MUSEUM, 1889. 



and numerous smaller specimens of smoothed or scratched rocks from 

 the New England States and Greenland. 



Forming a part of this series are also photographs of the glacial 

 potholes at Archbald, Pennsylvania (38294), and of a large drift bowlder 

 on the northern end of Deer Isle, Maine (37413). There are also smaller 

 views showing fields covered with drift bowlders. 



LIFE. 



The collections illustrating the destructive effect of life in its various 

 forms are at present writing sadly lacking in desirable materials. A few 

 poorly selected stones bored by mollusks (No. 29644-29649) aud a fria- 

 ble sandstone riddled by the holes of a hymenopterous insect (37641) 

 constitute about all that is worthy of mention. The constructive effects 

 are better showu by the diatomaceous earths (37429), marls (36850 and 

 70034), shell limestones (35814 and 37749), chalk (36013), guano (69281), 

 and the peats aud coals (36826). 



The method of formation of a coral island is in this series shown by 

 a small collection illustrative of the geology of Bermuda. The exhibit 

 begins with a collection of the more common corals and shells of the 

 island, aud which by their disintegration have furnished the bulk of the 

 materials of which the islands are composed. These include bottles 

 which, having lain for two years in the water, are covered by a growth 

 of millepora alcicornis, and which illustrate the rapidity of the coral 

 formation. Following these are specimens of the corals and shells 

 common to the neighboring waters, and the fine calcareous sand which, 

 resulting from their disintegration, is thrown by the waves upon the 

 beaches, dried, and drifted inland by the winds. Following these are 

 the rocks which result from the consolidation of these fragmental mate- 

 rials, a consolidation brought about by the dissolving action of water 

 on the calcium carbonate of the shells and a redepositiou of the dis- 

 solved materials at greater depths below the surface to form a cement 

 binding together the grains. Following these are the soils aud residual 

 clays; surface and weathered rocks illustrative of the characteristic 

 roughness of the coast; stalactites and stalagmitic masses resulting 

 from the deposition of dissolved lime in the numerous caverns with 

 which the island abounds; the exhibit closing with a series of rocks 

 foreign to the islands, but which occur occasionally as small pebbles, 

 having been drifted from other sources, and presumably entangled in 

 the roots of trees. For most of the materials in this collection the 

 museum is indebted to Prof. William N. Rice and the late Dr. G. W. 

 Hawes. 



III. — STRUCTURAL GEOLOGY: THE ARCHITECTURE OF THE EARTH'S 



CRUST. 



Under this head are displayed stratified rocks showing (1) stratifica- 

 tion and ics accompaniments, as forms of bedding, surface markings, con- 

 cretions, and such other illustrations as lend themselves readily to 



