418 Reviews — Radiolarians, etc., in Pre- Cambrian Rocks. 



of these, probably the oldest fossils known, was intrusted to M. L. 

 Cayeux, who has had considerable experience in the study of Radio- 

 laria and other microscopic organisms in the Cretaceous rocks ; and 

 the first of the above papers contains the results of a careful in- 

 vestigation into the nature of these bodies from an examination of 

 numerous sections of the rocks in which they are preserved. 



From the geological sections of the country drawn up by Dr. 

 Barrels no doubt can be felt as to the horizon of the fossiliferous 

 beds, which are bands of phtanite from half-an-inch to over three 

 feet in thickness, interstratified with the schists. The phtanites are 

 now principally of crystalline silica, and a certain amount of carbon- 

 aceous material is also present in them. 



The bodies described as Radiolaria are irregularly distributed in 

 the phtanites, sometimes occurring singly, at others great numbers 

 are closely associated together, so as occasionally to be in actual 

 contact. They are exceedingly small in size — the figured forms 

 range from -001 mm. to '022 mm. in diameter — and to observe their 

 structures it is needful to use much higher object-glasses than those 

 required for other fossil and recent Eadiolaria. By far the larger 

 number are simply spherical in form, some are ellipsoidal, and there 

 are many varieties of the inflated or cyrtoidal bell-shaped forms. 

 One or more radial spines occur in several forms, and in two or 

 three an inner concentric shell connected by rays with the outer 

 test has been detected. Most of the forms figured have holes or 

 perforations in the outer test, thus showing a lattice-like structure. 

 This is considered by the author to be present in all, though not 

 always recognisable. 



The author has figured 45 different forms of these minute bodies, 

 and the greater number ai'e assigned to different known Eadiolarian 

 genera, 19 in all; a few forms cannot be placed in any described 

 genus, but all are comprised in four of the great subordinal divisions 

 of Haeckel, viz., Sphseroidea, Prunoidea, Discoidea, and Cyrtoidea. 

 The author thus confidently asserts the close relationship of these 

 Pre-Cambrian forms to existing and other fossil Eadiolaria. 



It will readily be conceded that, at a first glance, the forms which 

 the author has had figured on the accompanying plate by an artist 

 unacquainted with these organisms (and therefore unbiassed) present 

 a strong prima facie resemblance to known Radiolaria. Certain 

 objections have, however, been made to placing them in this group 

 by some who have had the opportunity of seeing sections of the 

 rock containing them, and the author has very fairly and candidly 

 stated these objections and replied to them in the paper. It should, 

 perhaps, be mentioned that the figures now given have been taken 

 from specimens lately obtained by the author, which show their 

 characters more distinctly than in those which came under the 

 notice of the objectors. 



One objection is based on the extremely small size of the Pre- 

 Cambrian bodies as compared with the dimensions of undoubted 

 Radiolaria. This difference is A^ery striking under the microscope, 

 and it may be expressed by the fact that the average diameter of the 



