To this rule of the linear arrangement of the volcanic vents of the globe and their accumulation along certain well-marked bands, there are two very striking exceptions, which we must now proceed to notice. In the very centre of the continent formed by Europe and Asia, the largest unbroken land-mass of the globe, there rises from the great central plateau the remarkable volcanoes of the Thian Shan Range. The existence of these volcanoes, of which only obscure traditional accounts had reached Europe before the year 1858, appears to be completely established by the researches of the Russian traveller Semenof. Three volcanic vents appear to exist in this region: the active volcanoes of Boschan and Turfan or Hot-schen, and the solfatara of Urumtsi. At a point situated about half-way between these three volcanoes and the sea, another active vent, that of Ujung-Holdongi, is said to exist. Other volcanic phenomena have been stated to occur in the great plateau of Central Asia, but the existence of some at least of these appears to rest on very doubtful evidence. The only accounts which we have of the eruptions of these Thian Shan volcanoes are contained in Chinese histories and treatises on geography; and a great service would be rendered to science could they be visited by some competent explorer. [Sidenote: EXCEPTIONALLY-SITUATED VOLCANOES.] The second exceptionally-situated volcanic group is that of the Sandwich Islands. While the Thian Shan volcanoes rise in the centre of the largest unbroken land-mass, and stand on the edge of the loftiest and greatest plateau in the world, the volcanoes of the Sandwich Islands rise almost in the centre of the largest ocean and from almost the greatest depths in that ocean. All round the Sandwich Islands the sea has a depth of from 2,000 to 3,000 fathoms, and the island-group culminates in several volcanic cones which rise to the height of nearly 14,000 feet above the sea-level. The volcanoes of the Sandwich Islands are unsurpassed in height and bulk by those of any other part of the globe. With the exception of the two isolated groups of the Thian Shan and the Sandwich Islands, nearly all the active volcanoes of the globe are situated near the limits which separate the great land- and water-masses of the globe--that is to say, they occur either on the parts of continents not far removed from their coast-lines, or on islands in the ocean not very distant from the shores.