Geology and Mineral Resources of Paraguay A Reconnaissance

60lower third of the series consists largely of yellow tocream fine-grained sandstone, crossbedded in places,and with some intercalations of shale. The sandstoneunits are thin-bedded near the base but become thickerbeddedupward. The middle third of the series consistslargely of sandstone in thin beds; they are shalythroughout and become more so up\vard. Theseargillaceous beds, characterized by lilac, purple, andyello\v colors, contain ferruginous concretions inplaces. The upper third of the series is friable, yellowish-whiteto purple micaceous sandstone in thin beds.It contains intercalated varicolored shale in placesbut the sandstone tends to be considerably coarser ingrain than the lower units. This unit has yielded mostof the fossils reported from the series.The author's random observations along the highwaybetween Eusebio Ayala and San Jose confirm Harrington'sthree-fold division of the series in a general way.and add a few details as to parts of the section. Thehighway mentioned crosses the series diagonally fromits base to its top, so that the following notes must bein approximately the correct stratigraphic order.From a point 4.6 kilometers southeast of EusebioAyala to the broad valley of Arroyo Yhaguy, 5 kilometerswrest of Itacurubi de la Cordillera, the mainhiglrvvay traverses rolling grasslands marked by lightcoloredsoils. Several road cuts present excellentexposures of a small part of the section traversed (seefig. 48). In these, the rocks are seen to consist ofalternations of buff to light-reddish-brown soft shaleand very shaly micaceous sandstone in beds 1 to 5centimeters thick. A few of the beds, notably someof the micaceous sandstone, contain poorly preservedfossils.Alluvial material masks the Devonian rocks in thevalley of Arroyo Yhaguy where the main highwaycrosses it, but the beds are fatfly well exposed a shortdistance south of the highway in the vicinity of theMinas-cue or "Lopez" sulfur deposits. These depositsconsist of widely scattered concretions of marcasite inshale. The enclosing rock, which doubtless correspondsto Harrington's shaly middle part of the Itacurubiseries, consists of alternating beds of blue-gray shaleand mudstone, with local splotches of red and pink.The shale is sparsely fossiliferous.There are no good exposures along the highway nearItacurubi but \valls, buildings, and piles of rock invarious places suggest that there is a nearby source ofFIGUKE 48. Minor thrust fault in sandy micaceous shale of the Itacurubi series, Devonian age. View eastward on the highway 6 kilometers southeast ofEusebio Ayala. The beds at left have been pushed up and over the horizontal beds at right.