Reviews — Dr. T. Sterry Hunt's Chemico- Geological Essays. 555 



4. Purely chemical and mineralogical essays. 



Some of these essays have appeared in the columns of this 

 Magazine, and we may, therefore, suppose that many of our readers 

 are familiar with them ; but as the first and second group of essays 

 deal with subjects which have been provocative of constant and 

 progressive discussion, a brief notice of some of the points on which 

 they touch may not be without interest. 



Chemical and dynamical speculations, etc. — A vision of chemical 

 cosmogony is presented to us about the period in the general 

 history of Kosmos, when the partially cooled globe — our planet — 

 began to settle down to what must always be a subject of interest 

 to a geologist, viz. the formation of the nearest approach to rocks 

 we can conceive. Two principal hypotheses have been maintained 

 with respect to this consolidation. 1. That of a solid crust resting 

 on an uncongealed nucleus. This is perhaps the view which has 

 been most generally believed. 2. That solidification commenced at 

 the centre, and advanced towards the circumference, but that at the 

 close of this process a condition of imperfect liquidity supervened, 

 resulting in the formation of a superficial crust which retained a 

 liquid zone between itself and the solid centre. This portion of 

 uncongealed matter would be the seat of volcanic action, the evident 

 facts of a flexible crust requiring something of this sort. 



In the lecture which he delivered at the Royal Institution in May, 

 1867, " On the Chemistry of the Primeval Earth," Dr. Sterry Hunt 

 adopted the theory of a solid crust, partly on the grounds that " numer- 

 ous and careful experiments show that the products of solidification 

 (always excepting water) are much denser than the liquid mass." 

 To this view the late lamented David Forbes took exception, as 

 indeed he did to almost every point in our author's lecture. The 

 consequence of this was a somewhat embittered controversy carried 

 on between these eminent geological chemists, for the most part in 

 the pages of this Magazine. That was a time when few persons 

 in this country availed themselves of chemistry and the allied sciences 

 in the study and grouping of the rock-masses ; a time when almost 

 any rock that was green might be put down as a " greenstone," and 

 when the numerous analyses which had been made on the Continent 

 and in America were almost unknown to our geologists. The return 

 of David Forbes from a long sojourn in foreign countries was marked 

 by a not unsuccessful effort on his part to assert the importance of 

 chemical geology. He thus acquired great and well-merited influence 

 in fashioning and controlling opinion in this country on all points 

 relative to the chemistry of rocks. 



Although doubtless Dr. Sterry Hunt laid himself open to 

 criticism in some respects, as, for instance, when he states that "quartz 

 can only be generated by aqueous agencies and at comparatively low 

 temperatures," it may be questioned whether Forbes was particularly 

 happy in his criticisms or in the reasons by which he sought to 

 enforce them. Let us take, for instance, his appeals to the results 

 seen on a small scale in the cooling of melted metals ; where, as 

 observed by Hunt, the conditions of a liquid congealing in an atmo- 



