514 Notices of Memoirs— Prof. E. Hull — Glacial Epoch. 



part of the Lauren tian, in the scarcely-defined " Algonkian " group 

 of the United States Geological Survey. 



Below the Huronian is the Upper Laurentian or Grenville system, 

 consisting of gneisses and schists (some of which, as Adams has 

 shown, have the chemical composition of Palaeozoic slates), along 

 with iron-ore, graphite, and apatite, and great bands of limestone, 

 the whole evidently representing a long period of marine deposition, 

 in an ocean whose bed was broken up and in part elevated before 

 the production of the littoral elastics of the Huronian age. It is in 

 one of the limestones of this system that, along with other possible 

 fossils, the forms known as Eozoon Canadense have been found. 

 The author did not propose to describe these remains, but merely to 

 exhibit some microphotographs and slices illustrating their structure, 

 referring to previous publications for details as to their characters 

 and mode of occurrence. 



Below the Grenvillian is the great thickness of orthoclase gneiss 

 of various textures, and alternating with bands of hornblende schist, 

 constituting the Ottawa gneiss or Lower Laurentian of the 

 Geological Survey. No limestones or indications of fossil remains 

 have yet been found in this fundamental gneiss, which may be 

 a truly primitive rock produced by aqneo-igneous or •' crenitic " 

 action, before the commencement of regular sedimentation. 



The author proposed, with Matthew, to regard the Etcheminian 

 series and its equivalents as pre-Cambrian, but still Palaeozoic ; and, 

 as suggested by himself many years ago, to classify the Huronian 

 and Grenvillian as Eozoic, leaving the term Archaean to be applied 

 to the Lower Laurentian gneiss, until it also shall have afforded 

 some indications of the presence of life. 



He insisted on the duty of palaeontologists to give more attention 

 to the pre-Cambrian rocks, in the hope of discovering connecting 

 links with the Cambrian, and of finding the oceanic members of the 

 Huronian, and less metamorphosed equivalents of the Upper 

 Laurentian, and so of reaching backward to the actual beginning of 

 life on our planet, should this prove to be attainable. 



III. — Another Possible Cause of the Glacial Epoch. By 

 Professor Edward Hull, LL.D., F.K.S., F.G.S. 



ri^HE author gave an account of the results ai'rived at by Professor 

 JL J. W. Spencer, Ph.D., in his memoir on "The Keconstruction 

 of the Antillaean Continent" (Bull. Geol. Soc. America, January, 

 1895), from observations laid down on the Admiralty charts of the 

 east coast of North America and the shores of the West Indian 

 Islands and Gulf of Mexico. He shows that the " continental 

 shelf " lying between the coast and the 100-fathom line is succeeded 

 by a second and deeper plateau, called by Professor A. Agassiz 

 " the Blake plateau," the average depth of which may be taken at 

 2,700 feet, separated from the continental shelf by a steep descent, 

 and in its turn bounded by a second steep descent leading down to 

 the abysmal depths of the Atlantic Ocean at 12,000 or 13,000 feet 



