Revieius — Coal-fields of Colorado. 29 



convenient to adopt the suggestion of Messrs. Brydone and Griffith to 

 include this lower part of tlie coranguinum chalk in the zone below. 

 As regards the Upper Chalk, too, the author was led independently 

 to recognize the existence of two separate stages, which were 

 subsequently established by Mr. Jukes-Browne (Geol. Mag., Dec. V, 

 Vol. IX, pp. 304-13, 360-72). The paper contains interesting 

 observations with respect to the depth at whicli the various deposits 

 were laid down, and the remarks on the Starfish fauna of the cuvieri 

 zone at Branscombe (Devon) bear out the views of Messrs. Jukes- 

 Browne and Rowe that a Greensand ridge existed in the neighbour- 

 hood of the Hooken, as is shown also by Sherborn. 



Measurements of numerous ossicles have been taken with a view to 

 discussing variation. It is shown that isolated sapero-marginal 

 ossicles can be taken as trustworthy indications as to the size and 

 relative height of the individual. It is pi'obable also that a high 

 ossicle may represent some physiological advantage to the starfish, 

 since the marginalia border the visceral cavity, and therefore an 

 increase in height would allow greater space for the digestive organs 

 and the gonads. In considering variations in a lineage Mr. Spencer 

 adopts as a unit the tangent of height to length (of a supero-marginal 

 ossicle), which he calls the ossicular angle, and the results are 

 expressed grajihically. The continuousness of variation sliown to 

 exist would render zonal work difficult but for the coexistence of 

 other independently variable characters. Periodic elaboration, to 

 which attention has been drawn in other groups by Bernard, 

 Buckman, and Lang, is also traced. All races pass through parallel 

 stages, and some variations must be regarded as predetermined ; of 

 some, in fact, the course could be predicted. 



Apart, however, from its theoretical interest the paper has gi'eat 

 practical value in that the collector can determine with a degree of 

 certainty the isolated ossicles that are commonly found. Considering 

 the unpromising nature of the material, Mr. Spencer's results are 

 extremely encouraging to the palseontologist. 



V. — United States Geological Surveys. 

 1. Coal Fields of Grand Mesa and the West Elk Mountains, 

 Colorado. By Willis T. Lee. pp. 237, with 21 plates and 

 37 figures. Bulletin 510. 1912. 



THIS bulletin contains a description of all the mines in the various 

 districts and a discussion of the general geology and stratigraphy, 

 illustrated by a geological map on the scale of 2 miles to the inch. 

 The section on the quality of the coal contains over eighty analyses 

 of samples. 



The coal-fields of this area occur on the southern edge of a great 

 basin in Western Colorado and Eastern Utah. The lowest beds 

 exposed are shales and sandstones of the Gunnison formation, regarded 

 as Jurassic in age. An unconformity separates these beds from an 

 Upper Cretaceous series, whicli attains a thickness of some 6,000 feet 

 and includes all the coal-bearing beds. The base of this series is 

 formed by the Dakota Sandstone, which is overlain by the Mancos 

 shale, containing coal of poor quality near the base, and fossils 



