286 



SCIENCE. 



[N. S. Vol. VII. No. 165. 



pated that the experiments bearing upon these 

 points would be detailed and the conclusions 

 to be drawn from them pointed out. In this 

 way it would have become much clearer how 

 much or how little experimental work had done 

 in elucidating the development of the frog, and 

 the book would have been given a unity which it 

 does not now possess. The descriptive portions 

 and the account of experimental work might 

 have been bound under separate covers, neither 

 volume showing a decided lack of the matter 

 treated in the other. It may be questioned if 

 a volume on the general subject of 'Experi- 

 mental Embryology,' from so competent a hand 

 as that of Professor Morgan, with no attempt 

 even nominally to limit the discussion to a par- 

 ticular egg, would not have met the demand 

 more precisely than the present work. The 

 descriptive chapters will hardly take the place 

 of Marshall's work on the embryology of the 

 frog, and this portion of the book seems in 

 some respects not so well presented as that on 

 the experimental results. In some chapters the 

 arrangement is a confused one. Thus, after 

 an extended discussion of the cleavage of the 

 egg and especially the variations in that process, 

 and after the egg has been brought to the 

 blastula stage, we find again (p. 41) a para- 

 graph adding some new facts as to the first and 

 second cleavages. At times one misses a clear- 

 cut statement of the question upon which a set 

 of observations or experiments bear. For ex- 

 ample, in the account of Roux's experiments 

 with oil-drops, pp. 43-47, it is mentioned only 

 incidentally that the question here is as to the 

 part played by surface tension in cleavage, so 

 that the point might easily be missed by one 

 not acquainted with previous discussions on the 

 subject. In the descriptive chapters typo- 

 graphical and other errors also are more fre- 

 quent ; a particularly confusing matter is the in- 

 correct reference in the text to the lettering of 

 the figures, in a number of cases. Thus occurs 

 on p. 41 (' Fig. 12 G. H.'), p. 105 (' A'-B^' and 

 'Fig. 33 B'), p. 156 ('Fig. 47 B'). In several 

 cases the discussion would be made much 

 clearer if the successive cleavage planes could 

 have been numbered in the figures. 



The descriptive part, however, whatever be 

 its merits or demerits, is not the distinctive 



feature of Professor Morgan's book ; it is for 

 the account of experimental, work that it will 

 be read, and for this it will be found of the 

 greatest value. 



Heebbet S. Jennings. 

 Montana College of Ageicultuee and Me- 

 chanic Aets, Bozeman, Montana. 



Geologic Atlas of the United States, Folio 36. 



Pueblo, Colorado, 1897. 



The folio consists of seven pages t f text, 

 signed by Grove Karl Gilbert ; a topographic 

 map ; maps showing the areal geology, economic 

 geology, structure sections, deformation and 

 data pertaining to artesian water ; a sheet of 

 columnar sections, and a sheet showing typical 

 fossils and special types of outcrop. The scale 

 is 1 : 125,000, and the area described is com- 

 prised between parallels 38° and 38° 30' and 

 meridians 104° 30' and 105°. 



The quadrangle includes a portion of the 

 Great Plains close to the base of the Rocky 

 Mountains. The topography is partly of the 

 foothill type and is in general sufficiently rug- 

 ged to exhibit clearly the stratigraphy and 

 structure. In the western part are portions of 

 the great hogback formed by the upturned edge 

 of the Dakota sandstone. 



The formations range from Archean to Pleis- 

 tocene. The Paleozoic rocks have a thickness 

 of but two or three hundred feet and their ex- 

 posures are unimportant. The Juratrias rocks, 

 comprising bright-colored shales and sandstones, 

 have an extreme thickness of 2,500 feet, but 

 their surface extent is small. The Cretaceous 

 rocks range from the Dakota formation to the 

 Pierre and cover nine- tenths of the area. They 

 consist chiefly of gray shale ; in a total thick- 

 ness of 3,800 feet there are only 75 feet of lime- 

 stone and 300 to 500 feet of sandstone, the latter 

 being at the base of the series. One hundred 

 feet of alluvial sand and gravel are referred to 

 the Neocene, and other alluvial deposits to the 

 Pleistocene. 



Unconformities appear at the base of the 

 Paleozoic, Cretaceous, Neocene and Pleistocene 

 formations, and the geologic history is cor- 

 respondingly complex. The structure of the 

 Paleozoic and Juratrias rocks was ascertained 

 only in the limited area of their exposure. The 



