MANGANESE OXIDES AND MANGANESE NODULES IN MARINE DEPOSITS. 731 



of manganese on some of the stones at the water-line were 3 or 4 inches in thickness. 

 The nodules varied in size from 2 inches to ^s °f an mcn m diameter, and all showed a 

 concentric arrangement of parts. The general appearance of the stones and nodules is 

 shown by the sections in figures 1, 2, 3, and 4. 



Fig. 1. — Schistose Boulder from the Barrier, Loch Goil, T \ natural size. A, boulder of Mica schist. B, layers of 



Manganese dioxide. 



Fig. 2. — Section of Loch Striven Nodule (natural size). 

 The layers of Manganese dioxide (B) have been de- 

 posited round a piece of slate (A). 



Fig. 3. — Section of small Nodule from 

 Loch Goil (natural size). 



Fig. 4. — Section of Boulder of Schist from Loch Fyne, showing Manganese Deposit (^ natural size). 

 A, boulder of schistose rock. B, layers of Manganese dioxide. 



The chemical composition of these nodules differs only slightly from that of those 

 taken in the deep sea, and this difference arises from the greater abundance of mineral 

 particles and their different nature, quartz and other continental minerals being almost 



