FRANCIS— ON CASSAVA. 
115 
Explanation of Diageam. 
Fig. 1 shows approximately the lines of the principal dislocations 
which have affected the older rocks of Trinidad, and produced the 
Gulf of Paria and the Bocas. 
Fig. 2 is a diagram showing the probable extent of the subsidence 
by which the Bocas and Gulf of Paria were produced. 
Fig. 3 shows the general succession of the rocks of Trinidad — a 
b, g, d, Caribean Group ; e, compact limestone ; f, secondary rocks ; 
ff, eocene of Tamana and Manzanilla ; g\ eocene of Sanfernando ; h, 
miocene of Guaracara ; h\ miocene of South Naparima : li\ miocene, 
of Couva, Savanetta, Pointe Noir, etc. ; k'", miocene and pliocene of 
Moruga, Mayaro, etc. ; i, post pliocene or detrital series. 
* Principal dislocations or faults. 
Figs. 4 and 5 are referred to in Mr. Wall’s report. 
III. — On Cassava. By Ernest Francis, F.C.S. 
It is well known that two species of the euphorbiaceous 
plant manioc or cassava are said to exist ; one of which, 
called bitter cassava, possessing poisonous qualities, is 
avoided in its fresh and dangerous condition ; while the 
other, or sweet cassava, being considered harmless, is 
largely used as food in its natural state. 
The noxious properties of bitter eassava have been com- 
mented on by numerous medical and toxicological historians 
since the time of Piso, who in the middle of the seventeenth 
century mentioned, together with other facts, the toxic 
powers of the radix mandihoca : the true nature of the 
poison, however, became established only at a much later 
date. 
In 1796, Dr. Clarke of Dominica, describing the fatal 
effects resulting to negroes from drinking half-a-pint of the 
2 
