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Derby.] - 1 - < ^ [Feb. 21, 



think it pro-table thai they will yet be found on the Tocanlins. On the op- 

 posite or northern side of the valley, they occur close to the margin of the 

 river, in the vicinity of AJenguer, in front of Santarem, and extend for a 

 considerable distance towards the north, along the rivers Curua, Maecuru 

 and Trombetas ; to the west, they extend at least as far as the Uatunni, 

 already mentioned, and to the east, as far at least as the .lauary, near the 

 village of Prainha.* 



The rocks consist of soft shales and sandstone, and of limestone, which last 

 although of but slight thickness, is the; most important, because, having 

 resisted denudation better than the other rocks and being highly fossilifer- 

 ous, it forms an admirable base of reference in the study of the Carbonifer- 

 ous series. The best exposures of the limestone are on the Tapajos, both 

 above and below the village of Itaituha, where it is quarried to burn for 

 lime. The thickness is about twenty-five feet, some of the beds being of 

 very pure limestone, of a blue or light brown color, others being darker and 

 somewhat argillaceous and silicious. The fossils being silicified, and conse- 

 quently more durable than the rock In which they are enclosed, become 

 detached by the slow dissolution of the limestone, and often appear loose, 

 as on the beach in front of Itaituha. Cherty masses are common in the 

 limestone, and aside from these, two other kinds of chert occur in loose 

 masses which, in the opinion of Mr. Smith, come from some unknown 

 beds above the limestone. One of these kinds decomposes to a white, 

 chalky mass, the other, which forms large, rounded boulders in front of 

 Itaituha, takes on, in decomposition, the appearance of a porous sandstone. 

 Cherts of various kinds are very abundant in the whole Carboniferous 

 region, and are often highly fossil iferous, but the beds from which they 

 originate are as yet unknown. 



Above the limestone at Itaituha, there are beds of soft, brown sandstone 

 and of shale, of unknown extension, and below there is a heavy series 

 of green, red and black shales, some of which contain Spirophyton and are 

 most probably Devonian. Of the Carboniferous rocks of the Mauhe-assu, the 

 only notices we have are of the limestone, which is identical in character 

 and fossils with that of the Tapajos. Passing now to the northern side, we 

 find a thick bed of limestone at the foot of the Serra of Tajuri, in the 

 Erere region, where it is associated with a yellowish mottled sandstone, 

 much appreciated by the people for whetstones. The exposure, however, 

 in this locality is so unsatisfactory, that it was impossible to determine its 

 relation to the other beds of the serra. In the region between the Maecuru 

 and Curua, there are exposed, over an extensive area, a variety of beds, 

 which .Mr. Smith attempted to arrange in a section which, although some- 

 what defective, is of considerable interest. 



* In this sketch of the character ami extension of the Amazonian Carbonifer- 

 ous, I have, aside from tin- observations of Prof. Harttand myself, drawn largely 

 from tin' excellent studies of .Mr. Smith on the northern side of the Amazonas, 

 and am also indebted to Mi'. Coutinho, the first discoverer of Amazonian fos- 

 sils, and to Messrs. I ihandless, Brown ami Ilodrigues, for notices of its existence 

 in regions, not visited by the members of the < teological < lommission. 



