1818.] Neighbourhood of the River Zaire. 221 



although a few of them have been found in the southern parts of 

 the temperate zone. Mr. Brown remarks, that some, or the 

 whole of these plants, may be conceived to have been originally 

 natives of only one of these countries, and may have been con- 

 veyed to the other either by accident or design ; but he offers 

 many considerations which render it probable that with respect 

 to the greatest part of them this is not the case. 



As to the proportion of new genera and species in Prof. 

 Smith's collection, we have already stated the general facts in a 

 note attached to the sketch which we gave of his life. The 

 additions which he has made to our botanical knowledge are 

 indeed very considerable ; and when we reflect upon the short 

 space of time which he spent in the country, and the unfavour- 

 able circumstances which attended the expedition, it cannot 

 but impress our minds with a very high idea of his zeal and 

 activity, and with the deepest regret for his premature death. 



Article XIII. 



Analyses of Books. 



Transactions of the Geological Society, Vols. III. and IV. 



{Concluded from p. 139.) , 



1 . Observations on the Geology of Northumberland and Durham. 

 By N.J. Winch, F.L.S. 



This paper contains a very interesting account of the strata 

 which occur in the counties of Northumberland and Durham ; 

 of which the following is a brief summary, beginning with the 

 uppermost or newest of the series. 



1. Red Marl. — This rock is seen on the north bank of the 

 Tees, forming an irregular curve from near Darlington to the 

 mouth of the river. It consists, as usual, of alternating beds of 

 white, grey, and red calcareous sandstone, of red and blue slaty 

 clay, and of gypsum. Borings to the depth of 120 fathoms 

 have been made in this rock in an ineffectual search after coal. 

 The springs arising from the blue marl of this deposit are not 

 unfrequently impregnated with sulphuretted hydrogen. 



2. Magnesiau Limestone.^ — The country lying immediately to 

 the north and west of the boundaiy of the red marl is of magne- 

 siau limestone. It forms the entire coast from Hartlepool to 

 South Shields, and is seen coming up on the back of the coal 

 strata along an irregular line from Shields to the Wear at Pallion, 

 and thence running S.W. to Sellaby on the Tees. 



The beds of this rock are thin, and are seen crossing slips and 

 fractures in the subjacent coal strata without themselves under- 

 going any change; hence Mr. W. infers that the period of the 

 deposition of this rock was subsequent to the disturbance. 

 3 



