G. J. Brush on Amhlygonite from Maine. 243 



are described as three small islands (probably islets of one atoll) 

 containing but little guano and that much mixed with coral sand, 



Christmas Island is a well-known lagoon thirty miles long, 

 trending east and west, having much vegetation. Much has 

 been said by speculators of its rich deposits, but I have good 

 reason to believe that there is no guano, worthy of mention, on 

 the island. Samples that I have examined were chiefly coral sand. 



Starbuck's, Starve or Hero Island is an elevated lagoon, and 

 is worthy of mention because, like Jarvis', McKean's and other 

 islands of similar structure, it contains a large deposit of gypsum. 

 Its supposed guano I have found to consist of the hydrated sul- 

 phate of lime, containing about twelve per cent of phosphate of 

 lime and colored by a little organic matter. 

 _ So far as my observation extends, all elevated lagoons have 

 similar deposits of gypsum. 



As regards the distribution of these phosphatic guano deposits 

 I believe them, in this region of the Pacific, to be confined to 

 latitudes very near the equator where rain is comparatively of 

 rare occurrence. In latitudes more remote from the equator 

 than 4° or 5° heavy rains are frequent, and this circumstance is 

 not only directly unfavorable to the formation of guano deposits 

 tut it encourages vegetation, and when an island is covered 

 ^ith trees and bushes, the birds preferring to roost m them, 

 there is no opportunity for the accumulation of guano deposits. 



New York, August, 1862. 



Art. XXl,~ Contributions from the Sheffield Laboratory of Yale 



CoUege.~llL On Amhlygonite from Hebron in Maine ; by 



George J. Brush. 



A FEW weeks since Mr. John M. Blake, Ph.B, late assistant 

 in this Laboratory, called my attention to a peculiar feldspathic 

 looking mineral kssociated with the lepidohte^ from Hebron, 

 Maine. Mr. Blake found on blowpipe examination that the 

 mineral was extremely fusible, and that it gave a strong reaction 

 for hthia, coloring the flame beautifully crimson. A t^rttier ex- 

 amination has shSwn it to be a phosphate of alumina and l.th.a, 

 ^ith a considerable amount of fluorine and some water This 

 composition, together with its physical properties. Have tea me 

 to refer it to the rare species am6%omte. , «„„« ^^m'tA 



LepidoUte occurs at Hebron in large masses m a^^.^f ^.g^^^^^^*^' 

 and ihe amhlygonite is found imbedded in^his lep.dolte asso- 

 ciated with aibite, quartz, red, green -"^^.^l^tracTvar^'ty of 

 more rarely with cassiterite, and a peculiar compact variety o^ 

 apatite containing minute prismatic crystals oi a hair-Dro«n 

 mineral, which I have not yet been able to obtain in sufficient 

 quantity to determine fully its characters. 



