V2 PROCEEDINGS OF THE ACADEMY OF 



March 2. 

 The President, Dr Ruschenberger, in the chair. 

 Twenty-eight members present. 



On Thin Sections of the Traps of the Mesozoic Basin. Prof. 

 Frazer made the following remarks: The great mesozoic basin 

 traverses York, Adams, Chester, and Montgomery Counties, in 

 Pennsylvania, as well as New Jersey and New York, while de- 

 tached portions are found in several of the New England States, 

 in none of which are its characteristics more clearly defined than 

 in Connecticut. During a recent visit to New Haven I had the 

 privilege of examining the fine microscopic slides or thin sections 

 which have been prepared by Mr. Dana from the traps of that 

 region. It is of great interest to observe the striking resemblance 

 of these rocks to our own from the same formation. To the eye 

 and even under the magnifying glass they seem the same, whereas 

 in fact they are of, at least, two different kinds. 



One kind, which has been described on several occasions before 

 the Academ} 7 as that forming the Seminary Ridge near Gettys- 

 burg, is a greenish-gray compact dolerite (projected by me on the 

 screen by means of the gas microscope, at a previous meeting), 

 which, under higher magnifying power, shows white tablets of 

 >lagioclastic felspar and green ciystals of pyroxene, with some 

 chrysolite (olirinej. 



Far different is the rock which has been previously referred to 

 as Sj*enite, and which has an apparently similar representative 

 near New Haven. Under the microscope, however, the coarse 

 rock from New Haven resembling the others from that locality 

 in everything but texture, differs materially from the specimen 

 from Gettysburg. 



Since my return home I have examined two or three other slides 

 of the Gettysburg rock, and find no essential difference between 

 them. They contain hornblende and quartz; the others do not. 

 The constituents of the coarse rock from both States were pyrox- 

 enite, plagioclase, maguetite, some chrysolite, some bictite, and 

 rarely quartz. 



The investigations of the last week have led me to query the 

 occurrence of prehinite in this rock which I reported at the last 

 meeting. But these questions will be settled very soon. 



The death of Rev. Henry S. Spackman was announced. 



