442 V. F. MARSTERS — ASBESTOS DEPOSITS OF BELVIDERE MOUNTAIN 



words, these facts show that the amphibolite has been absorbed by an 

 intruded igneous rock. The somewhat slaty and baked character of the 

 amphibolite on the immediate contact bears out this conclusion. In 

 sections of the serpentine at a short distance from the contact the fibrous 

 aggregate structure appears again as in the normal type from other parts 

 of the area. 



It should be stated here that the above contact was at first regarded 

 as a simple fault.* That crushing of the serpentine, as well as the am- 

 phibolite, has taken place is admitted ; but if the contact is of the nature 

 of a fault alone, brecciation should form a prominent factor in the thin- 

 section. This does not appear, but the phenomena of absorption and 

 infusion of the amphibolite are the prominent features. The fracturing 

 of the serpentine and the adjacent hornblendic rock is to be attributed to 

 a subsequent movement, with which was associated the deposition of 

 the asbestos. 



APPLICATIONS OF EMERSON'S VIEWS 



An alternative is to be considered in discussing the probable origin 

 of the serpentine. It has been shown by Professor Emerson that ortho- 

 rhombic p3^roxenes develop in limestones by processes of metamorphism 

 and also along contacts of igneous or intrusive masses with lime-mag- 

 nesia rocks. The question therefore arises with regard to the Belvidere 

 serpentine. Might not the bastite (enstatite) in this case represent a transi- 

 tion stage in a rock, originally sedimentary, high in lime and magnesia 

 and containing a variable percentage of iron ? It has been shown by 

 Professor Emerson f that the above relationships occur in Old Hampshire 

 county, Massachusetts. Moreover, it should be stated that this area lies 

 in the same geological province with the Belvidere area. Emerson also 

 demonstrates that not only the serpentine is derived from the pyroxenic 

 calcareous rocks, but that the amphibole rock — amphibolite — is also a 

 metamorphic product derived from the same series. In other words, 

 both the serpentine and the amphibolite are, according to his interpreta- 

 tion, secondary products resulting from processes of metamorphism of 

 magnesia-bearing limestones, and not of igneous or intrusive masses. 

 The succession of changes from the original sedimentary rock to the 

 final secondary products, as suggested by Emerson, are shown in the 

 following tabulated scheme : 



*The crushed and broken character of the serpentine observed in the region of the contact on 

 the Tucker property was regarded as sufficient evidence of a true fault, and was so stated in the 

 Preliminary Report of the Vermont Geological Survey, 190M904, page 96. Further detailed study 

 of thin-sections makes it reasonably certain that the crushing of the rock was a subsequent 

 phenomenon, which provided favorable conditions for the depositions of the "cross-fiber." 



f Monograph xxix, U. S. Geol. Survey, pp. 78-117. 



