THE NONMETALLIC MINERALS. 459 



face thoy are covered with a tliinner or thicker close-sticking whitish, nearly chalky 

 crust, whicli exhibits on many pieces veins or network, while in most instances it 

 covers the surface like an earthy powdery coat. Tlie surface of fresh-broken pieces 

 appears conchoidal, with finely radiating' lines in each conchoidal impression. The 

 luster is glossy, the mass is hard and transparent to a certain depth, and where 

 scrati'hed with a knife or needle it leaves a white powdered stroke. It can easily 

 l)e scraped with a knife into powder which, if sprinkled over red-hot coals, changes 

 instantaneously into thick vapors, at first with a slight yellow color, with a strong 

 aromatic smell, somewhat similar to that of incense. Large pieces brought into con- 

 tact with a light soon burn up, developing at the same time the above-mentioned 

 vapors. When chewed it crackles between the teeth without leaving a noticeable 

 taste. 



The fact that there is often seen, even on the canted broken sides of many pieces, 

 the same hard, whitish, earthy crust which covers the other unbroken surface of the 

 same i)iece, tends to prove that after their falling off the mother tree they were 

 forcibly transported from their original spot by floods or earth falls, by which they 

 were broken before they came into the marl or sandy plains in which they are now 

 found. At times the crust just alluded to is very hard, of considerable thickness, 

 and with a glossy polish, which leads to the supposition that pieces in which it is 

 found have been embedded for a long time in the ground, or perhaps in water basins. 

 While an earthy crust of greater or less thickness is noticed on all pieces of gum 

 copal before it is washed or rubbed off, the color in different pieces varies very much; 

 some samples are yellowish white, some of honey or gold color, and others are dis- 

 tinguished by an intense reddish orange color. The general appearance of the pure 

 pieces of this resin, especially in the gold-colored kind, has delusive resendjlance to 

 amber, with which, though much softer, it has the common properties of igniting 

 and of becoming electrical by friction. The interior of the Angola copal pieces, 

 when not mixed with earthy substances, or with remains of bark, is even glossy and 

 transparent; but I have never observed insects in any of the numerous samples 

 which, partly in Angola and partly at Lisbon, came under my notice, while in the 

 copal sent to Lisbon from the province of Mozambique, on the east coast of Tropical 

 Africa, various hymenopterous insects are to be met with. The different colors of 

 the copal of Angola just described are connected more or less with its availabihty 

 for varnishes, etc. Thus the copal dealers distinguish three sorts, namely, ( 1 ) red 

 copal gum (gomma copal vermellia) ; (2) yellow (g. c. amarella); (3) whitish 

 (g. c. bianca). The red and whitish sorts furnish the best and finest varnish, and 

 therefore are most in request and the dearest, while the whitish quality is sold at 

 the lowest price. ^ 



According- to Burton ' the present limit of distribution of the gum- 

 yielding trees on the east coast is less extensive than that of the extinct 

 forests which have yielded the true or "ripe" copal, or "sandarusi," 

 as it is locally called. Every part of the coast from Ras (lomani, in 

 south latitude 3, to Ras Delgado, in 10° 41', with a mean depth of 30 

 miles inland, may be called the copal coast. The material is found in 

 red, sandy soil, but is not evenly distributed, occurring rather in 

 patches, as though produced by isolated trees. Dr. Kirk considers 



' Journal of the Linnean Society of London, Botany, IX, 1866, pp. 291-293. 



'' Lake Region of Central Africa, II, p. 403. See also report by Dr. M. C. Cooke 

 on the gums, resins, etc., in the India Museum, or produced in India. London, 

 India Museum, 1874. 



