BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



VOL. 16, PP. 91-130, PLS. 24-32 MARCH 10, 1905 



PLUMOSE DIABASE AND PALAGONITE FROM THE HOLYOKE 



TRAP SHEET* 



BY B. K. EMERSON 



(Presented before the Society December 30, 190 If) 

 CONTENTS 



Page 



Extent, thickness, and general structure of the trap sheet 92 



Types of foreign inclusions in the diabase 92 



Meriden type : Blending of mud and lava at the base of the bed 92 



Titans Pier type : Blending of mud and sand with the lava at the surface 



of the bed 93 



Holyoke Reservoir type : Blending of mud and lava in the central portion 



of the sheet 95 



General statement 95 



Description of the area 95 



The normal diabase . . 95 



Resume of the structure of the abnormal area 96 



Abstract of theory of formation of plumose forms and of palagonite . 96 



Detailed descriptions 97 



Central explosion breccia 97 



Occurrence of analcite 98 



General description of the schlieren 98 



Varieties of the schlieren rocks 99 



Long plumose diabase 99 



Short plumose variety with remelted pyroxenes . 100 



Glass-bearing porphyritic diabase 101 



Gabbroid diabase 102 



Description of the palagonite f 103 



Botryoidal glass with radiate fibrous devitrified layers 104 



Spherulites, sphaarocrystals, and lithophysEe in the glass 105 



The lithoidal or holyokeite base 106 



The holyokeite or diabase-aplite dikes 107 



A composite dike 108 



Quaternary veins of quartz, of calcite, and of tuff Ill 



♦This paper is published by permission of the Director of the United States Geological Survey. 

 A friend called my attention to the interesting exposures made in clearing the surface of 

 the trap for a new reservoir, and I asked my assistant, Mr Walter L. Allen, to examine the 

 place. He discovered the interesting plumose trap and the glass described below and collected 

 much of the material for the investigation, and has taken part of the photographs used in the 

 paper. I owe the drawings to the skill of my daughter, Mrs Charlotte E. Hitchcock. 



XIII— Bull. Geol. Soc. Am., Vol. 1G, 1904 (91) 



