ECONOMIC GEOLOGY. 283 



The application of chemical analysis to the determination of the 



elementary constitnents of soil may also he included under the head 



of economic geology. Its utility is manifest, since the comparison 



of the composition of virgin soil with those cultivated, and of others 



exhausted, will readily show what elements are extracted by certain 



plants, and consequently what substances should be contained in the 



manures applied by the cultivator to regenerate his estates. 

 • 



Such are the principles which the surveyors appointed to report on 

 the economic geology of Trinidad liave kept steadily before them in 

 the execution of their task. In those respects in which they have 

 failed to accomplish the ends indicated above, they trust such defects 

 will be ascribed not to a deficiency of zeal on their part, but rather to 

 the limited means at their disposal ; to the difficulties opposed to 

 works of this nature in tropical countries, where many facts of vital 

 importance to correct conclusions are unfortunately concealed, or ob- 

 scured by the depth of the soil, and where the examination of localities 

 remote from lines of regular traffic is attended with a considerable 

 expenditure of time. 



The district examined is comprised between the islands at the Bocas 

 on the west, and the hills above St. Joseph and Ancona Valley on tlie 

 east. In meridianal extension it ranges from the plain of Caroni to 

 the northern coast. Passing visits were also made to Cedros, Point-a- 

 Pierre, and the Pitch Lake, for the satisfaction of the late governor, 

 Sir Charles Elliot ; but the observations were not sufficiently detailed 

 to justify description. The following remarks will therefore relate to 

 the first named section of the country only. 



The geological structure of this district consists of a metamorphized 

 strata, probably underlaid by gneiss, which nowhere comes to the 

 surface in Trinidad, but is the rock forming the point of Paria on the 

 adjacent coast of the main land. 



This metamorphic series may be divided into the following mem- 

 bers : 



A. Dark blue, sometimes nearly black limestone, laminar, or com- 

 I^act, not generally crystalline or micaceous, but traversed by nume- 

 rous veins of calc spar, (carbonate of lime ;) it occurs in layers inter- 

 stratified with shale containing laminar gypsum, and sometimes thin 

 beds of sandstone. This limestone deposit forms the island of Pato, 

 near the coast of the main land, the island of Gasparillo within the 

 gulf, and the southwest portion of the Laventille hills. This is the 

 uppermost number of the series, and has an average dip to the south at 

 a>'ariable angle. The beds are sometimes horizontal, at others nearly 

 vertical. Numerous faults traverse these districts, and the limestones 

 are at times much shattered. This division, as well as the succeeding, 

 are entirely unfossiliferous. 



B. A series of beds, consisting of clay slates, sandstones, subordi- 

 nate mica slates, and a number of shales, often talcose ; but little 

 limestone appears in the group ; when i)resent its texture is crystal- 

 line. Extensive segregations of quartz have been induced between 

 tlie laminas of the beds of this system, often attaining a width of two 

 to three feet ; contortions are frequent, cleavage imperfect and irregu- 



