GEOLOGY IN NATIONAL MUSEUM — MERRILL. 287 



Effects of lightning. — Lightning striking in loose sand often so 

 fuses the material in the immediate vicinity of its path as to form 

 irregular tubes rough on the outside, but smooth and glassy within. 

 These are called fulgurites; they may vary from a few inches to 

 many feet in length, but are too brittle for preservation in any but 

 short sections. Lightning striking on firm rock may melt it on the 

 immediate surface or even bore small holes entirely through it, as 

 in the samples from the Elk Mountains of Colorado and Mount 

 Ararat, Armenia. 



The transporting power of wind and ocean currents. — This is 

 shown by a series of jars containing wind-transported material like 

 volcanic dust from Krakatoa and other localities, and loess deposits 

 from the United States and China. 



Mud and ripple marks. — Mud and ripple markings made during 

 deposition of sediment in shallow waters, and mud cracks due to 

 shrinkage on drying are shown on large slabs of sandstone and 

 quartzite from Ohio, New York, and Pennsylvania. 



Sedimentation on sea bottoms. — This is shown by samples of 

 dredgings from various oceanic depths. Of particular interest is a 

 series of separations into their component parts of soundings in the 

 Pacific Ocean by the U. S. steamship Nero. 



Collection illustrating the geology and minerology of the District 

 of Columbia. — The areas occupied by the various geological forma- 

 tions, crystalline and fragmental, are shown by a relief map. The 

 region, as a whole, is very poor in rock types, minerals, or fossils. 

 What few minerals are found occur almost wholly in the crystalline 

 rocks of the northwest section. The collection shows all the forms 

 thus far discovered. 



HISTORY OF AMERICAN GEOLOGY. 



In the aisle at the end of the hall are two flat cases containing 

 collections relating to the history of American geology, and including 

 portraits of the early workers and copies of their published works. 



Reserve or study series. — During the work of the various govern- 

 mental surveys, and to a less extent State and private surveys, there 

 have accumulated and been assigned for preservation in the National 

 Museum a very large number of collections of rocks and ores which 

 are grouped in part under kinds, but to a large extent preserved as 

 collections representing the studies of particular areas, the results of 

 which have been published in detail. These are not on exhibition, 

 but constitute the reserve or study series referred to elsewhere. 



The following list includes some of the more important of these 

 collections : 



Anthracite-Crested Butte quadrangle, Colorado, Folio 9, U. S. Geol. Survey. 

 Apishapa quadrangle, Colorado, Folio 186, U. S. Geol. Survey. 



