14 GEOLOGICAL MEMOIRS. 



remarked, that the contortions of the Trilobite-beds are slighter than 

 those in the fifth system and the remaining parts of the fourth. 



After enumerating the places where the coal-bearing beds may be 

 seen to dip under the slate and quartzite of the fourth system, and 

 describing the appearance of the rocks at each place, he states that 

 near the summit of Monte Alto the contorted shale of the second 

 coal-group may be seen reposing unconformably upon the beds of 

 the fourth system, and notices similar appearances of unconformity 

 in other localities between the coal-beds and the Trilobite-slates. 



Although he considers these and other similar facts sufficient to 

 correct the erroneous idea of the age of the coal-beds which their 

 position would at first cause to be entertained, he again calls atten- 

 tion to the fact mentioned at p. 13, that, while in some places the 

 Trilobite-beds border the Coal-series, as at Cancella velha, at others 

 they occur at some distance apart ; and he also states that on the 

 banks of the Rio Ferreira, near the brook of Boloi, the beds of the 

 second system are immediately succeeded by those of the fourth, 

 without the occurrence of any of the members of the Coal-series, 

 while this does not occur in passing from the strata of the fourth 

 system towards the Trilobite-beds. 



And if to all these facts we add the one already referred to at 

 pp. 9 & 12, that the conglomerate of the Coal-series is mostly formed 

 of pebbles of slate and quartzite identical in character with those 

 rocks of the fourth system ; and also bear in mind that, while the 

 Silurian fossils are generally distorted, in consequence of the con- 

 tortion and compression of the beds, the fossil plants of the Coal- 

 series, and especially those of the first group, are beautifully pre- 

 served ; as well as the fact of the beds of the last-named group not 

 being at all disturbed, though those of the second group are slightly 

 so, but in a much less degree than the Silurian quartzite, — the fol- 

 lowing conclusions may be drawn : — 



1. The Silurian slate existed prior to the formation of the coal- 

 beds, and formed the sides of the basin in which they were deposited. 



2. The second group of these beds appears overlying the first, 

 through the inversion of the former. Consequently the overlying 

 second group is the older of the two, and they are both covered by 

 the still older Silurian rocks. 



It is therefore seen, from the visible line of strike of the several 

 systems, and from the undulations of the strata into anticlinals and 

 synclinals whose axes are in the same direction (namely N. 20° E.), 

 that a parallel overthrow has taken place, through which the beds now 

 lie in an inverted order to that in which they were originally de- 

 posited. We also see that the heaving operation of the granite, 

 while it exercised an immense lateral pressure upon the rocks, 

 pushed together the beds into a smaller space than they originally 

 occupied. 



The investigation of the stratigraphical relations of those rocks 

 shows us that the principal contortions took place before and during 

 the deposition of the Trilobite-beds ; and the complete absence of 

 the Upper Silurian strata, which are represented in the neighbour- 



