Smithsonian Report, 1948.—Holmes PLATE 2 
1. Wave-swept surface of folded rocks, metamorphosed and partly granitized, 
representing the worn-down roots of a pre-Cambrian orogenic belt (about 
1,060 million years), at Borga, south coast of Finland. 
Photograph by Prof. C. E. Wegmann. 
2. Left, pleochroic halo in mica from Murray Bay, Quebec, showing well-devel- 
oped rings due to a-particles shot out from a uranium-bearing crystal at the 
center; right, pleochroic halos in a flake of brown mica from a Pre-Cambrian 
granite (about 1,030 million years) from Ontario, Canada. 
Photomicrographs by Prof. G. H. Henderson. 
