152 PROCEEDINGS OF THE ALBANY MEETING 



MICROSCOPIC STRUCTURAL FEATURES OF THE BANDED GLACIAL SLATE OF 

 PERMO-CARBONIFEROUS AGE AT SQVANTUM, MASSACHUSETTS 



BY ROBERT W. SAyLES * 



{Abstract) 



During the last year a microscopic study of the glacial slate at Squantum, 

 Massachusetts, has revealed many features which point to the seasonal nature 

 of the banding, A number of microscopic sections of this banding, taken from 

 specimens from Squantum and several other localities in the Boston basin 

 where this slate is exposed, were exhibited. 



A number of photographs, showing in a comparative manner the 

 banded clays of the Connecticut Valley and the Squantum slate, were 

 also exhibited. 



Presented by title and discussed and illustrated in the exhibition room. 



WEATHERING OF ALLAN ITE 

 BY THOMAS L. WATSON 



{Abstract) 



Allanite occurs in many localities in the eastern United States in massive 

 form and fairly abundant. Where found above water-level in the belt of 

 weathering, the lumps and masses of allanite have frequently undergone par- 

 tial decomposition exteriorly from weathering and are invariably coated partlj' 

 or wholly with usually a reddish brown crust, at times of lighter color, of 

 variable thickness. In some localities the weathered product exhibits a layered 

 structure — an inner reddish brow layer and an outer lighter colored very thin 

 layer which may be almost white in some specimens. In the larger lumps and 

 masses the thin weathered crust is sharply defined from the larger central 

 mass of fresh mineral. 



Some of the more important localities have been studied in the field and 

 collections made of the fresh allanite and its alteration product for laboratory 

 study. Microscopic study of the weathered product from many eastern locali- 

 ties shows it to be heterogeneous in character, composed of an isotropic type 

 and a weakly birefracting type, both variable in physical properties and prob- 

 ably in composition. Likewise the ordinary black, vitreous, fresh allanite is 

 shown microscopically to be a mixture of isotropic and birefracting types, the 

 latter derived from the former either by alteration or by inversion, probably 

 by alteration. Chemical analyses have been made of the fresh allanite and its 

 alteration product from localities in Amhert, Nelson, and Roanoke counties, 

 Virginia, and the changes involved in the transformation from fresh to de- 

 composed mineral are discussed. 



Presented by title. 



^ Introduced by J, B, Woodworth, 



