376 Reviews — The American Journal of Science. 



escaped denudation, to the fourth place of decimals of the proportionate 

 length of a petal, each and every detail seems to suffice for specific 

 separation. Surely one of the first and most essential parts of the 

 curriculum of a larval systematic palaeontologist should induce him 

 to collect, measure, and specifically distinguish every several leaf 

 from a well-grown tree. After such preliminary training, the ardour 

 of the image might he appreciably subdued. 



The present paper has two distinct merits above many of its kind. 

 Only two new species and two smaller divisions are named ; and 

 a concise index to their relative stratigraphical occurrence is supplied. 

 But the characters on which the specific and varietal divisions are 

 made do not appear to be of great importance, and no attempt is 

 made to demonstrate their meaning, if any. The latter criticism may 

 well be answered by the explanation that sufficient material is not yet 

 available ; but such an excuse would tend to suggest that the whole 

 matter might be left alone until such material has been collected. 



In two long-ranged forms like Scutella gabbi and Astrodapsis 

 tumidus there will be, in all probability, a progressive series of modi- 

 fications into well-marked directions. Until the trend of the variation 

 can be postulated, would it not be safer to defer the introduction of 

 new names which have no certain biological significance, and which 

 may lead even stratigraphers astray ? 



H. L. H. 



IY. — The American Journal oe Science. 



VOL. XXXIX of the American Journal of Science, 1915, contains 

 three important papers emanating from the Carnegie Institute 

 and dealing with the crystallization, under laboratory conditions, of 

 certain silicate mixtures. The first, by Mr. C. A. Rankin, describes 

 the ternary system lime-alumina-silica. Although the compounds of 

 these substances show no solid solutions, nevertheless the relations 

 are very complex, owing to the large number of minerals that 

 are possible: these are quartz, tridymite, cristobalite, corundum, 

 wollastonite, sillimanite, and anorthite, together with several calcium 

 silicates not known to occur in nature. The equilibrium diagram 

 contains no less than fourteen separate fields. The chief application 

 of the results is to the study of Portland cement. A subsidiary point 

 of geological interest is the observation that eutectics of silicates have 

 in general no structure differing from that of other mixtures, except 

 that they are very fine in grain. This is of some significance in 

 connexion with certain igneous rocks. In another paper Mr. Olaf 

 Andersen describes the system anorthite-forsterite-silica. In some 

 mixtures spinel is found to be a primary phase, while in others the 

 unstable substance clino-enstatite is formed. This is not a true ternary 

 system and can only be expressed in terms of the four-component 

 system lime-magnesia-alumina-silica. It is shown that under certain 

 conditions forsterite undergoes resorption without any change of 

 physical environment, a fact which has an important bearing on the 

 magmatic resorption of olivine in certain peridotites and anorthite 

 rocks. When the olivine becomes surrounded by a shell of its 



