1855.] 331 



and is there associated with Lutraria Traslii, Conrad, also a new species. Im- 

 pressions of very small crabs have been fonnd in this rock, and I have also 

 seen wh^t appeared to be the marks of fucoides on the surfaces of ihe layers. 



A stratum of the Monterey formation similar in texture to the stone which is 

 used for building, but different in color, also contains casts of Tellina congesta 

 in great numbers. The color of this rock is a dark olive green or brown, but 

 when it has been weathered the surface is white. When it is dry it is very 

 light and adheres to the tongue, being very absorbent. Though soft and easily 

 cut with a knife it is very tough, and gives a ringing sound when struck by a 

 hammer, like a well baked tile. 



In addition to the Tellina and other fossil shells which this rock contains, it 

 is charged with innumerable and beautiful Polythalamia, (Foraminifera, D'Or- 

 bigny.) lying in thin layers through the mass and becoming visible in white 

 lines on the edges of the slabs. They may be seen with the naked eye, but the 

 assistance of the microscope is required to trace the forms of those that happen 

 to be exposed. They are very w r hite and perfectly preserved, and are exceed- 

 ingly beautiful objects for the microscope. It is, however, to be regretted that 

 the material in which they are preserved is so indurated and resisting that it is 

 impossible to get them out for study. Every cross fracture of the rock pre- 

 sents innumerable sections, and occasionally the full form of a shell is visible 

 on the surface. 



The rock has another interesting peculiarity, which must be mentioned it is 

 bituminous, and gives off an empyreumatic odor when it is heated before the 

 blowpipe flame. The specimens which I have are perforated by Petricola cylin- 

 dracea and other boring shells. 



The upper stratum of the formation at the quarries, which is overlaid by the 

 beach shingle before mentioned, is worn smooth and uneven, as if it had been 

 subjected to the action of the surf. It has been perforated by Tholadidce., and 

 their cells still remain. They are large and numerous, but no shell could be 

 found in them. They are tilled up with fine sea-sand, which indicate that the 

 shells must have been removed before the surface emerged from the tide. The 

 cells are in all respects similar to those now being formed and occupied in the 

 rocks of the beach. 



This locality is now at an elevation of about sixty feet above the beach and 

 one quarter of a mile from it. It presents convincing evidence of the compara- 

 tively recent elevation of the coast. 



The connection between the strata of siliceous infusoria and the strata con- 

 taining the Polythalamia has not been traced, but it is probable that the two 

 deposits are conformable, and parts of one great series. If this is so, we may 

 conclude that the intervening strata are also charged with fossils. The forma- 

 tion, so far as already known, is a wonderful record of life, and a rich mine of 

 results for the geologist and palaeontologist. 



Characteristics of some New Species of Mammalia, collected by the IT. S. and 

 Mexican Boundary Survey , Major W. H. Emory, U. S. A. Commissioner. 



By Spencer F. Baird.* 



PART I 



Sciurus limitis, Baird. Size less than that of S. migrator! 'us. Upper molars 

 four. Fur very short, compact and close pressed. Ears long, coated with very 

 short hairs. Feet small ; soles naked, and dark brown. 



Color. Above, mixed cinnamon and black. Under parts of body and tail, 

 cinnamon. Tail above and on the sides like the back, with three annulations of 

 black. Head and body 10 inches. Tail mutilated. Hind foot, from heel, 



* Full descriptions of these species will shortly appear in the official reports 

 of the Survey. 



