Febbuaet 10, 1911] 



SCIENCE 



233 



carry the Cretaceous-Tertiary parting witli a 

 fair degree of accuracy from the actual con- 

 tact at the Arroyo del Caballero on the Rio 

 Grande to a similar contact at Eamones, forty 

 miles east of Monterey, and from Panalito 

 on the Conchos Eiver to the southern bound- 

 ary of the state of Tamaulipas. We hope to 

 fill the gap between Eamones and Panalito 

 before we finish. 



Numerous sections were made of the over- 

 lying Eocene to the eastward of this line of 

 contact and good collections of fossils were 

 made from various horizons in it, which prove 

 that the substages recognized in Texas con- 

 tinue south as far as we found any deposits 

 of this age. We were able to map approxi- 

 mately the areal distribution of each of these. 



The highly fossiliferous deposits on the Rio 

 Grande which constitute the upper member of 

 the Cretaceous of that region and which are 

 known as the Escondido beds, only continue 

 southward in this character for forty miles to 

 a point southwest of Laguna de la Leche, 

 where they are covered by much later de- 

 posits. Where these later deposits end near 

 the Salado river west of Rodriguez we find 

 underlying them, in place of these fossilifer- 

 ous beds, beds of blue shale without fossils, 

 which have the same relation to the overlying 

 Tertiary that the Escondido has through its 

 whole extent. These blue shales, which we 

 call the Papagallos shales, are therefore con- 

 sidered to be the extension or equivalent of 

 the Escondido and are found to extend south 

 to the limit of our investigations. To the 

 south, these blue shales draw nearer and 

 nearer to the coast until at their crossing of 

 the Zarziza in southern Tamaulipas there is 

 barely ten miles of Tertiary deposits between 

 the outcrop of the shales and the waters of 

 the gulf. 



On the Rio Grande and at several other points 

 between that stream and the Pesqueria we 

 found deposits of Midway age, as proved by 

 its characteristic fossils, resting directly on 

 the Cretaceous, but for the most part this 

 basal contact is covered or obscured by the 

 overlapping Carrizo sand. The last of the 

 Midway was seen at Ramones. 



When we again pick up the contact at 

 Panalito on the Conchos River, we find both 

 the Carrizo sands and Marine beds in contact 

 with the blue shales of the Cretaceous, while 

 a few miles down the river the Yegua over- 

 laps both of these and is the substage in con- 

 tact almost to the Soto la Marina. A few 

 miles north of this river, the Tegua, Fayette 

 and Frio are in turn covered by the San Fer- 

 nando beds and beyond that point we found 

 no further exposures of the Eocene. 



South of the Soto la Marina River the beds 

 of the Eocene seem to be entirely wanting, if 

 they were ever laid down. Our drilling rec- 

 ords as yet show no evidence of them, unless 

 some part of the blue shale on which the San 

 Fernandan rests be proved later to be of 

 Eocene age. No fossils have yet been found 

 in this shale, but its general character and re- 

 lations to overlying Tertiary as well as to the 

 Escondido and to other known Cretaceous de- 

 posits seem to warrant its reference to the lat- 

 ter period. 



The San Fernando beds, which are regarded 

 as Oligocene, were first observed at San 

 Fernando on the Conchos or Presas River and 

 have an extensive development to the south, 

 entirely overlapping or replacing the Eocene 

 deposits and resting directly upon the Cre- 

 taceous. This formation, with its beds of 

 nummulitic limestone and great numbers of 

 cristellaria, carries an extensive and varied 

 fauna and has a much greater development 

 than previously observed. It is succeeded by 

 other beds of similar composition, but of dis- 

 tinctly later age, which in turn overlap it and 

 reach the underlying Cretaceous shales. 



These later beds continue down the coast as 

 far as Tecolutla. They are well exposed at 

 Tuxpam, where they have a highly character- 

 istic fauna, including two very heavy oysters 

 which are nearly round. Both are of the same 

 general shape, but one of them has on one 

 valve four or five deep plications. The echin- 

 oderms of these beds are especially note- 

 worthy, there being probably eight species 

 in our collection. The most abundant form 

 is a Clypeaster which attains a diameter of 



