O. A. Lebour, and W. Mundle — Coal in Chile. 505 



of Quartz often replaced by grains of Hornblende, and inclosing here Ft. In. 

 and there crystals of Calc-spar and small particles of crystallized Iron- 

 pyrites 10 



37. A bluish-grey calcareous Sandstone, very hard and fine-grained, and 



much jointed, containing crystalline Dolomite in the partings . .10 



38. A strong grey argillaceous sandstone, slightly micaceous, coarse, with 



disseminated crystals of Hornblende and Chlorite 75 



59. A brownish shale mixed with coarse particles of sand . . , .13 



40. The Ninth and last <7o«Z-seam, of fair quality 2 



41. Greyish and bluish shales, scared in some places by red Oxide of Iron . 25 



42. A greenish-grey argillaceous sandstone, micaceous and fine-grained, 



containing many fragments of trunks of trees and ferns . . . . 2 10 



43. A light bluish-grey arenaceous shale, with scares of coal . . . .66 



44. Is a rock distinctly different from any of those we have passed through in 



this section ; this is a brownish -red argillaceous conglomerate, coarse- 

 grained, with various sized pebbles of White Quartz, Granite, Syenite, 

 Greenstone, Porphyry, Quartzite, etc 3 



45. A much stronger thick conglomerate, more compact than the last,- but 



with smaller sized pebbles, and consisting, in addition, of a large pro- 

 portion of micaceous and Chloritie rocks 210 



Total . , . 587 



This last stratum is in direct contact with, the metamorphic rocks 

 which form the mountain range, and the dividing ridges of the Coal- 

 district, and lies unconformably upon them. It does not enter within 

 the scope of this paper to treat more largely of these older mica 

 schists, chloritie schists, talcose slates, clay slates, etc. The section 

 we have given above will, perhaps, suffice to give one a correct idea 

 of the structural characteristics of the formation under consideration, 

 (see Fig. 2). The next point we shall advert to, is one of more 

 theoretical interest ; namely, the mode of deposition of these beds. 

 That they are in a great and preponderating measure of purely 

 marine, and in the minority of cases, at least, of estuarine origin, 

 may, we think, be safely inferred from the fossils which they 

 contain, and that these conditions very rapidly interchanged is, like- 

 wise, easily to be seen by the thinness and variety of the beds in 

 our section. The great and varying instability of the land during 

 the formation of these beds, which was the evident cause of this, is 

 little indeed to be wondered at, when we consider that a great 

 portion of that vast upheaval to which we owe the Andes was 

 actually going on at this very period, whether we take it to be a late 

 Secondary one, as has been suggested, we believe, by D'Orbigny and 

 E. Forbes, or whether, as Darwin thinks, it be one " verging on the 

 commencement of the Tertiary era." 



This alternation of the circumstances under which the deposition 

 took place leads us, with the help of a few collateral considerations, 

 to what we believe to be a true explanation of the dissimilarity, 

 before referred to, between the sets of beds on either side of the 

 ridges of older rock breaking their continuity. We are not aware 

 that this striking discrepancy between these neighbouring sections 

 has ever been explained, or even noticed, by any former observer. 

 Darwin remarks, that these formations have, in some cases, "appa- 

 rently been accumulated in troughs, formed by submarine ridges," 

 in others, that " the Tertiary strata seem to have been separately 

 accumulated in bays, now forming the mouths of valleys," but 



