150 THE MICROSCOPE. Oct. 



The Oldest Fossils, Microscopic. 



Hv ARTHUR M. EDWARDS. M. D. 



NKWARK, N. J. 



AboQt two years since, Dr. Charles Barrois announced 

 in a brief note to the " Comptes Rendus," the discovery 

 of Radiolaria in the Pre-Cambrian rocks of the horizon 

 of the mineral schists and phyllites of St. Lo, in the north 

 of Brittany, France. The further description of these, 

 probably the oldest fossils known, older than the Eozoon 

 Canadense, was intrusted to 31. E. Cayeux, who had con- 

 siderable experience in the study of Radiolaria and other 

 microscopic organisms in the Cretaceous works: and the 

 first announcement has just come to me from M. Cayeux. 



There can be no doubt with respect to the Pre-Cam- 

 brian rocks in the section where the Radiolaria were 

 found. There are bands of phthalate from half an inch 

 to over three feet in thickness, interstratified with schists. 

 The phthalate are principally crystalline silico and a cer- 

 tain amount of carbonaceous material is also present in 

 them. The presence of Radiolaria shows' that the car- 

 bonaceous material is organic matter like the carbona- 

 ceous material in the Laurentian rock where the Eozoon 

 is found. The Radiolaria is distributed in the phthalate 

 irregularily, sometimes occurring singly, at others in 

 great numbers closely associated together, so as occas- 

 sionally to be in actual contact. They are exceedingly 

 small in size — .001 mm. to .022 mm. in diameter — and 

 to observe their structures it is needful to use much 

 higher objectives than those required for other fossils 

 and for recent Radiolaria. 



By far the larger number are spherical in form ; some 

 are elipsoidal, and there are many varieties of the in- 

 flated or cyrtoidal bell-shaped forms. One or more ra- 

 dial sjjines occur in several forms and in two or three, 

 an inner concentric shell connected by rays with the 



