34 Bulletin 30 450 



parently Heneken erroneously inferred that the Monte Cristi sand- 

 stone was continuous with the Santiago sandstone (which we 

 have not seen) and that it underlay the entire Yaqui Valley. 



Calcareous Clays. — These form about three-quarters of the 

 total thickness of the section and contain casts of a number of 

 molluscs among which the following only could be determined : 

 Sconsia Iczvigata Sowerby, Strombus bifrons Sowerby, Olivella 

 muticoides Gabb, Natica cf. Youngi Maury, Chione Woodwardi 

 Guppy. Of these Sconsia Iczvigata is found in Zones A, B, E, F 

 of Rio Gurabo, Bluff 1 at Cercado and at Bowden ; Strombus 

 bifrons in Zones A, E, F, Bluffs 1 and 3 and Bowden; Olivella 

 muticoides in Zones G and H of the Gurabo and Cana rivers ; 

 Chione Woodwardi in Bluffs 2 and 3 and Zones H and I. Hence 

 two of the formations of the Yaqui valley seem to be represent- 

 ed on the Morro. 



The clays are gypsiferous, thin plates filling the cracks as in 

 the Scapharea patricia beds of the Cana river. 



Limestone Cap. — This is about two hundred feet thick, white 

 below, yellowish from weathering above. Casts of Pecten, Glyci- 

 meris and Conns were found but not specifically identifiable. 

 Corals were also present. Gabb followed Heneken in considering 

 this limestone to be a continuation of that capping the Samba 

 Hills, the intervening part having been removed by denudation. 

 The probability of this is greatly enhanced by our collecting 

 specimens of a coral, kindly identified for me by Dr. Vaughan as 

 Syzygophyllia dentata (Duncan), from both the Morro limestone 

 and that of the Samba Hills. This species also occurs in Zones 

 C and D, Rio Gurabo. 



Geological Notes on Scattered Localities 



Section on the Samba Hills at about 5 4.0 feet altitude. — On the 

 old road leading to the mines described in the route of our Ex- 

 pedition, Bulletin 29, pages 5 and 6, between Las Caobas and 

 Rompino, the following section was obtained. The aneroid had 

 not been reset for some time and the readings are approximate 



