40 Bulletin 30 456 



the conditions on the Gurabo and Mao the change in the mol- 

 luscan fauna on the Cana would come right above H in the unex- 

 plored region. That the change in the corals preceded the mol- 

 luscan change at first seems contradictory, but as Professor Har- 

 ris suggests, corals are extremely sensitive and would respond to 

 the change of conditons from its very inception. 



The few corals we obtained from the Gurabo and Mao river 

 bluffs do not show the break between F and G and G and 1 and 

 2 and 3. Apparently several of the species lived as did a num- 

 ber of the molluscs but there were only three or four corals in F 

 and G together and their evidence is outweighed by the hundreds 

 of species of molluscs and the Bryozoa and Foramanifera, all of 

 which agree in making a unit of Bluffs 2, 3, Zones G, H and I. 

 This unit is set off from the overlying Zones A-F and Bluff 1 

 unit. 



Dr. Vaughan considers that H is probably Chipolan ; D and 

 F, Alum Bluff above the Chipolan ; K and D, uppermost Alum 

 Bluff, i. e. uppermost Burdigalian ; and A-C, perhaps Helvetian 

 Miocene. According to Dr. Vaughan the Chipola and Alum 

 Bluff horizons are Oligocene. 



Formations of the Yaqui Valley. — The Tertiary clays and 

 limestones of the Yaqui Valley seem to the writer to represent 

 three well defined formations separated by marked changes in the 

 molluscan faunas. These formations may be designated as fol- 

 lows : 



3. The Sconsia Icevigata ~\ p orm . 



2. The Aphera islacolonis ( ation 



1. The Orthaulax inornatus ) 



In addition to these the presence of an older formation car- 

 rying Gabb's "Orbztoides" (perhaps Lepidocyclina) and constitut- 

 ing the Monte Cristi Range is suggested, but awaits investigation 

 in the field. Examination should be made of this range at var- 

 ious places, as on the trail near Alta Mira from Puerto Plato to 

 Santiago to determine whether Lepidocyclina is present and the 



