126 proceedings of the amherst meeting 



Sectional Meeting of Thursday Afternoon 



titles and abstracts of papers presented before the sectional 

 meeting of thursday afternoon and discussions thereon 



The section for the reading of petrologic papers met about 2 o'clock, 

 under the chairmanship of Vice-President Arthur Keith, with E. 0. 

 Hovey acting as Secretary, and listened to the following program : 



TUBULAR AMYGDALOID FROM XOYA SCOTIA 

 BY T. L. WALKER AND A. L. PARSONS 



{Abstract) 



The writers observed during the past summer a peculiar structure in the 

 basaltic rocks along the south shore of the Bay of Fundy, particularly a short 

 distance east of Morden, in Kings County, and at Margaretville, in Annapolis 

 County. At the former locality the reddish amygdaloid in the low cliffs along 

 the shore is penetrated by vertical cylindrical structures from one to four and 

 a half inches in diameter and at times at least two yards in length. The 

 material of these cylinders is characterized by the presence of white 

 amygdules of zeolites from an eighth to one-quarter of an inch in diameter, 

 which are more abundant near the margin of the cylinders than at the center, 

 while the main mass of the basalt is not marked by any prominent ainygda- 

 loidal structure. On a flat surface of basalt below high tide, where the rock 

 was perfectly exposed, the writers observed, within a radius of four feet, 

 twenty-five tubes, eighteen of them from one and a quarter to one and three- 

 quarters of an inch in diameter. The smallest was one inch, while the largest 

 was four and a half inches in diameter. The rock here shows no columnar 

 structure. 



Just west of the wharf at Margaretville the basalt is black and very coarsely 

 columnar. The columns, which are quite irregular, are separated by thin 

 seams of silica and are worn deeper at the center by the waves, so as to 

 constitute a series of saucer-like depressions with elevated rims. Here a 

 tubular structure of a different type is noted. It consists of hard vertical 

 cylinders from one to two inches in diameter, sometimes of quartz or quartz 

 and zeolites ; at other times of what appears to be a fine-grained, dark basalt 

 with occasional amygdules of quartz. These cylinders are not distributed 

 without regard to the columns, as there is a marked tendency for one core to 

 occur toward the center of each column, although in some instances a column 

 contains several cores, and a few cores may be situated on the margins be- 

 tween two columns. From these two localities How's original specimens of 

 mordenite were obtained. He states that it occurred in cylindrical concretions. 



In the former locality the best development of tbe tubes is in an amygda- 

 loidal flow some thirty feet thick, where they seem to have been the vertical 

 vents for ascending vapors from the wet underlying rocks. The Margaret- 

 ville type of cylinder might represent the result of liquid magma entering 

 chilled tubes from winch the steam had blown out all the liquid magma 

 available. 



