On the Structure and Position of Eozoon Ganadense. 281 



unknown. And the occurrence of these generic types in 

 strata very remote geographically, has served to identify them 

 geologically ; so that no doubt any longer remains that the 

 Upper Cambrian rocks of North Wales, the alum-schists of 

 Sweden, and the Potsdam sandstone of the United States (for- 

 merly ranking as the lowest member of the North American 

 Silurians) with an underlying series of slaty rocks extending 

 from New York to Newfoundland, belong to the same epoch 

 as the Bohemian strata supposed by M. Barrande to present 

 the earliest forms of organic life. 



But below the Tremadoc slates and Lingula flags which con- 

 stitute the Upper Cambrian, there is a vast series of sandstones 

 and slates, known as " Harlech grits " and " Llanberis slates " 

 (sometimes designated the ' ' Longmynd " group, from being the 

 components of the hills of that name in Shropshire), which 

 constitute the Lower Cambrian series. The organic remains 

 hitherto discovered in these are extremely scanty as regards 

 number of types ; consisting only of five species of Annelids 

 and one obscure Crustacean form in the Harlech grits, and two 

 species of the Zoophyte Oldhamia in the Irish equivalent of 

 the Llanberis slates. But the number of individual Annelids 

 whose remains are preserved is enormous ; they are stated to 

 occur in countless myriads through a mile in thickness in the 

 Longmynd. 



Of the immense lapse of time that must have been occu- 

 pied in the deposit of the Cambrian strata, both the nature of 

 their materials, which must have been derived from the dis- 

 integration of rocks of exceeding hardness, and their vast 

 thickness afford ample evidence. The Tremadoc slates are 

 estimated at 2000 feet, and the Lingula flags at 6000, making 

 8000 feet for the Upper Cambrian. Again, the Harlech grits 

 present a thickness of from 6000 to 7000 feet, and the 

 Llanberis slates about 3000, thus giving 10,000 feet as the 

 thickness of the Lower Cambrian.* The labours of our Ca- 

 nadian geologists have brought to light a - series of strata in 

 the neighbourhood of Lake Huron, and thence designated 

 Huronian, which are believed to be the equivalents of our 

 Lower Cambrian, and which attain a thickness of not less than 

 18,000 feet. These consist chiefly of quartz-rock, with great 

 masses of greenish chloritic slate, which sometimes include 

 pebbles of crystalline rocks belonging to the still older Lauren- 

 tian formation to be presently described. No organic remains 

 have yet been discovered in this series, but beds of Limestone 

 occur in it, one of them 300 feet in thickness; and as the 



* The above figures are those given by Sir C. Lyell. By Professor Phillips 

 the Longmynd strata are spoken of as " supposed to be 20,000 feet thick or 



