457' Dominican Sections — Maury 41 



relative age of the strata. 



1. No one knows where Gabb found his Orthaulax inornatus 

 because none of his Dominican fossils were labeled more precisely 

 than, "Miocene, Santo Domingo." We presume, however, that 

 it was collected from the basal blue clays in the Eastern part of 

 the Yaqui Valley where the Revolution prevented our securing 

 sections and collections. For in the Western part of the valley 

 we have gone almost to the contact of the Tertiary with the older 

 series (See crystalline outcrop near Sabaneta, Plate 2B, Bulletin 

 29) and although a special search was made for Orthaulax we did 

 not find it. No doubt the Orthaulax zone represents an older 

 horizon than from which we collected. 



2. To designate the formation comprising our Bluffs 2, 3, 

 Zones G, H and I, I have chosen Cancellaria (Aphera) islacolo?iis 

 (See Bulletin 29, p. 65, pi. 10, fig. 12a, b) of which the descend- 

 ant, A. tessellata, is now living in the Pacific. A. islacolonis after 

 occurring in the beds mentioned disappears abruptly. I have 

 never found it above the faunal break. Hence it seems a good 

 index fossil of the lower formation. 



3. Very characteristic of the upper formation and extending 

 into what may possibly be the Helvetian strata of A-C, is Sconsia 

 Icevigata, of which the nearest living ally is the deep water S. bar- 

 budensis. S. laevigata is present in A, B, D, E, F, Bluff 1 and the 

 Morro. I have never found it below F or Bluff 1. It seems the 

 best guide to the upper formation. 



The possibility that the upper part of the Sconsia formation 

 grades into the Helvetian Miocene, as suggested by Dr. Vaughan 

 and Dr. Jackson, is very interesting, but judging from the evi- 

 dence given by the molluscs, is exceedingly doubtful since the 

 bonds between A and B and Bluff 1 and F are very close. 



Suggested Analogies with Porto Rico. — Dr. Berkey in his Re- 

 connoissance of Porto Rico* found a great unconformity separat- 

 ing an Older Series of Cretaceous interbedded limestones, tuffs and 

 shales from a Younger Series of Tertiary shales, limestones and 

 sands, which range from the I^ares shales to the Pleistocene dune 

 *Ann. New York Acad. Sci., vol. 26, p. 6i, 1915. 



