240 BUREAU OF AMERICAN ETHNOLOGY [Bull, 177 
formula was used to compute the duration represented by each of the 
individual levels, but the results often showed considerable variation. 
Since there was no way of knowing which of these individual dura- 
tions was most accurate, the best solution seemed to be to take the 
average of the levels included within the interval and this was the 
figure used (tables J and K). To arrive at the total duration of 
the Phase, the averages derived for each of the successive intervals 
isolated on the seriation chart were added together. The same pro- 
cedure was then carried out independently using Yoché Plain as an 
indicator of change, and although there were slight differences in 
the subdivision of the sequence, the resulting total duration coincided 
well with that based on Kalunye Plain. The experiment was repeated 
using 10 percent and 15 percent differences in pottery type frequency 
as a basis for subdivision of the sequence. In the case of the Taruma 
Phase, the total length of occupation based on a 10-percent change 
interval gave the closest approximation to the known duration of the 
Phase. 
The intervals selected on the basis of a 10-percent change in pottery 
frequency are given on table J for Kalunye Plain and table K for 
Yoché Plain, together with the duration represented by each inter- 
val, calculated by averaging the individual durations of the levels in- 
cluded within it (Appendix, table 30). These two independent cal- 
culations give very similar results: a total duration of 209.6 years 
based on Kalunye Plain and 204.4 years based on Yocho Plain. The 
Taruma Indians are reported at the mouth of the Rio Negro in Brazil 
in A.D. 1670 and on the upper Essequibo River by A.D. 1771. This 
places their entry into British Guiana within an interval of 100 years. 
The tribe became extinct in 1925. The total duration of 204 to 210 
years estimated from rate of pottery change when converted into 
calendar dates places their arrival at between A.D. 1715 and 1721, 
or within the period designated by the historical evidence. 
TaBLE J.—Duration of the Taruma Phase calculated on the basis of a 10-percent 
change in frequency of Kalunye Plain 
Interval Duration 
in years 
WMrom WL Testis. oa ee ie a Rae 2G oo ee ne ene ee ee 
From E-30, Out 1, 8-16 cm. to E-19, Cut 2, 16-24 cm., inclusive. -.._..--.---------------------- 
From E-17, Cut 1 8-16 cm. to E-7, ‘Out uf 0-8 em., inelusive.,.224. se ae eee ee 
From E-9, ‘Cut its 16-24 cm. to E-16, Cut >, 8-16 cm., inclusive. i ~ dacs ites . sos ake 
From E-1, Cut 2; 8-16 cm. to E-7, Cut 1, 8-16 cm., inclisl Vee Lee 4h eal ae pied seal Pee 
From E- 29, Tests to E-30, Cut 1, 16-24 cm., Méelisivel VLC: ee OIL. WT Fe 
From E- 15, Cut 1, 8-16 em. to E-21, tests, Hnolaaive oct watt Bete PLC ui eee eat 
From E-13, Cut 1, 0-8 em. to E-10, Cut 1; 16-24 cm. inclusive ss bese chee 5. Se bee ee 
From E-1, ‘Cut 1 ‘8-16 cm. to E-7, Cut 2, 8-16 em., Anoluisive:_.2) ML CeeL ot.) wlikele an 
From E-18, Cut 1, 8-16 cm. to E- i, Cut 1, 24-32 cm., Inclusivec® {sees WE! Teese See AL oe 
From E-1, ‘Cut 2, 16-24 em. to E-6, Out 1416-24 emi inclusive: 622422202 es 2 ca ee ee 
From B-30, Cut Me 24-32 cm. to E-30, Cut 1, 40-48 cm., inclusive fos aee tee bos te ee eee 
From E-3, ‘Cut 1, ‘16-24 cm. to E-14 test, dincltsinge ee esis. Re eo hae achat es a 
fae pe ek ee arcrc) 
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