GEOPHYSICAL LABORATORY. 133 



The last-named silicates, on the other hand, were now found to include the 

 acid silicates, 2Ba0.3Si02 and Ba0.2Si02. This is a similar relation to that 

 known for the alkali metals, of which also the one having the lowest atomic 

 weight (lithium) forms the most basic siHcates and those with higher atomic 

 weights (potassium, etc.) more acid silicates. 



(468) A high-temperature regulator for use with alternating current. Howard S. Roberts. 



J. Opt. Soc. Amer., 6, 965-977. 1922. 



This apparatus is a modification, for use with alternating current, of the 

 author's direct-current furnace temperature regulator (J. Wash. Acad. Sci., 

 11, 401-409, 1921. Laboratory Publication No. 428). It is intended for use 

 with any sort of electrical heating device whose heating element has a reason- 

 ably high temperature coefficient of resistance and is not subject to accidental 

 changes of resistance. Its performance is about the same as that of the 

 direct-current apparatus. 



(469) A worked jade pebble from Copan. Henry S. Washington. J. Wash. Acad. Sci., 



12, 387-391. 1922. 



A jade pebble found by Dr. S. G. Morley during his excavations at the 

 Maya city of Copan is described. The pebble has been perforated to extract 

 disks for the making of ear ornaments and is sawn in two. Microscopic 

 examination shows that the "jade" is composed largely of albite, with less 

 diopside-jadeite. The preponderance of diopside over jadeite, brought out 

 by a chemical analysis, is unique among Middle American jades, with which 

 it is contrasted. 



(470) Deccan traps and other plateau basalts. Henry S. Washington. Bull. Geol. Soc. 



Amer., 33, 765-803. 1922. 



In this paper are described the so-called plateau basalts which, in various 

 parts of the earth, have issued from fissures and have covered numerous 

 areas with thick series of horizontal flows, which were evidently of great 

 fluidity. The basalts of the Deccan in India are described in considerable 

 detail on the basis of specimens from all parts of the area. The specimens were 

 furnished the writer by the Geological Survey of India. Of these, 11 new 

 chemical analyses are given. They are shown to be basalts of generally very 

 uniform composition, but are distinguished from most basalts of volcanic 

 cones by their high content in iron oxides and by certain mineralogical 

 peculiarities. The basalt flows of the Columbia and Snake River Valleys in 

 the northwestern corner of the United States (here named the Oregonian 

 region) are also described, along with several new analyses. These basalts 

 are shown to be closely similar in all respects — structurally, mineralogically, 

 and chemically — to those of the Deccan. 



The basalts of the so-called Thulean region are also described; this includes 

 the large, now mostly sunken, area of the North Atlantic, represented by 

 Iceland, parts of Scotland and its adjacent islands. East Greenland, Jan 

 Mayan, and Spitzbergen. A number of new analyses of basalts from Iceland 

 and the Faroe Islands are given, and it is shown that in general the Thulean 

 basalts are much like those of the Deccan. The plateau basalts of Siberia, 

 Patagonia, and the Lake Superior and eastern Atlantic regions in the United 

 States are also discussed. 



From these abundant data it is shown that the plateau basalts form a type 

 chemically and mineralogically different from the more common basalts that 

 issue from volcanic cones with explosive activity, and the general classifica- 

 tion of basalts is briefly discussed. The cause of the great fluidity of these 

 plateau basalts is attributed to their high content in iron oxides. 



