716 INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



The Moruga or arenaceous series is an extensive series of strata, usually of a loose sandy 

 nature. These are well exposed in cliffs all along the southern shore and offer some character- 

 istics quite peculiar to themselves and others which are possessed in common with the Caroni 

 division. Thick strata of massive sand, generally loose and pulverulent, are the most preva- 

 lent beds, and, indeed, sand may be said to be in great excess. Granular sulphur is very gen- 

 erally disseminated in these strata, having been observed from Canary round Point Icaque to 

 Oropuche. Shales are also numerous, but clays of rarer occurrence. 



Calcareous sandstone is extensively diffused in beds not exceediag 6 to 8 feet thick, and 

 often only a few inches, and, being very hard, resists the destructive action of the sea, running 

 out ia parallel lines on the beach often beyond low water, and forming quite a characteristic 

 feature of this line of coast. The cementing calcareous matter seems to have been comminuted 

 organic detritus, but in some cases the original nature of the deposit was fossUiferous sand, 

 the indistinct impressions of the shells remauiing, but their calcareous substance being entirely 

 removed and reprecipitated as cementing matter round the grains of sand, thus binding the 

 whole into one compact mass. * * * 



Layers of carbonaceous matter occur, but by no means so commonly as in the Caroni series. 

 The vegetable structure is usually very distinct, but occasionally obhterated. The principal 

 seam of lignitic shale is near Point Moruga. It occupies a vertical position and is 20 feet wide, 

 containing several layers of lignite not exceeding 10 inches but much inclined to be bunchy. 

 These carboniferous beds are all more or less mixed with shaly matter, rendering them impure. 

 At Erin and Irois the beds of lignite are less inclinded and the ligneous texture still more 

 apparent. 



Strata which will be named porceUanite occur especially at Erin, Points Cedros and Rouge, 

 part of Point Brea, to a small extent at Moruga, and adjacent to the large seam of coal at Punta 

 Paloma (Caroni series). By the above term it is intended to imply strata of semi to perfectly 

 indurated and compact structure, presenting a great variety of colors, among which brick-red 

 is predominant. They are fissured and jointed into almost cubical masses, these joints being 

 frequently lined with vesicular slag. An alternation of colors in thin laminas frequently prevails. 

 Some specimens are semivitrified, forming porcelain jaspers, and the fracture is frequently 

 cor^choidal. 



The peculiarities of these strata are most fully developed in the central portion, diminish- 

 ing in intensity upward and downward, and finally graduating into the adjacent shales or 

 sands. The thickness has not been noticed over 70 to 80 feet. 



This structure has been induced by the heat developed in the combustion of carbonaceous 

 matter, for not only are there remnants of the original stratum with its unconsumed carbon, 

 but this porceUanite is identically the same with the substances produced immediately above 

 or below seams of coal which have accidentally taken fire and burnt for a length of time. The 

 unconsumed portions are associated with granules of sulphur. Perhaps the decomposition of 

 pyrites (extensively disseminated in this series) generated sufficient heat to occasion the ignition 

 of the carbonaceous matter of the seams of lignite, and the cracks or fissures might permit so 

 much air to penetrate as would support a slow combustion. That this combustion originated 

 within the altered portions is evident from the circumstance of the adjacent lignitic beds being 

 unaffected,whichcouldnothavebeen the case had the heat been transmitted from below. * * * 



Natural asphalt, a well-known product of Trinidad, is extensively dissemmated in this 

 series. * * * 



No sections sufficiently extensive occur from which to deduce any very positive order of 

 succession; as far as could be ascertained, there seemed to be a great repetition of sands and 

 shales of very similar characters. 



The data for estimating the thickness are very uncertain; conclusions founded on the 

 inclined positions give at least 3,000 to 4,000 feet. 



