74 Scientific Intelligence. 
4, The Laccolitic Mountain Groups of Colorado, Utah and 
Arizona ; by @ Wuirman Cross. 14th Ann. Rep. U. S. Geol. 
Surv. Washington, 1895, p. 157-241.—This work represents a 
general summation of the author’s studies extending over a period 
of years upon the Anthracite and Crested Beetle districts of 
Colorado, where the opportunities for the study of laccolites on an 
extended scale are especially fine. In doing so he has been led 
to a general study of the literature upon this subject and has col- 
lated all the facts bearing upon the occurence of these intruded 
masses of igneous rocks in the plateau region of Western 
America so far as known. 
The paper opens with a review of Gilbert’s work in the Henry 
Mts. and with a definite restatement and affirmation of the prin- 
ciples laid down by that investigator. Following this the work 
of the earlier geological explorers in this region, especially Holmes 
and Peale, is reviewed, and it is shown that many of the detached 
mountain groups visited by them are to be referred to this mode 
of origin. The author then presents in detail the result of his 
own studies in the field mentioned above, and concludes with a 
general statement of principles. 
Especially valuable are the results showing the asymmetric 
form of laccolites when intruded into strata already flexed and 
under compressive stresses or tensional strains or containing 
resistant masses of former intrusion. It is of interest also to note 
the extremely uniform type of rock in these occurrences over 
such a vast range of country. Mr. Cross shows also that a cer- 
tain type of rock structure is a nearly constant resultant of the 
processes involved. It is impossible to say more of this work 
here than that it is a very valuable contribution to general dynam- 
ical geology and the writer feels from his own experience that 
it will be of distinct service in solving many problems in connec- 
tion with the occurrence of igneous rock-masses. ‘The paper is 
illustrated with many diagrams, sketches, photo-engravings and 
contains a geological map. i Your 
5. A Petrographical sketch of Aegina and Methana,; by H. S. 
Wasuineton. Journal of Geology (Chicago), vol. ii, No. 8, vol. 
ili, Nos. 1 and 2, 1895.—This paper contains a careful and detailed 
study of the igneous rocks occurring in a limited area in Greece. 
It is accompanied by a geological map and possesses many facts 
of interest to petrologists. It is especially valuable in being 
accompanied by a large number of excellent analyses which 
enable the author to discuss the region from a broad standpoint 
of general petrology. It thus possesses distinct features of 
general interest beyond those of petrographic detail. _L. V. P. 
6. Geologische und geographische Hxperimente ausgefiihrt mit 
Unterstiitzung der K. Akademie der Wissenschaften von Ep. 
Reyer. III, Heft, Rupturen. IV, Methoden und Apparate. 32 
pp. with 12 plates. Leipzig, 1894 (Wm. Engelmann).—The 
author continues in this small volume his earlier investigations 
and gives interesting results and conclusions drawn from them 
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