252 NOTICE OF THE OOLITIC FORMATION IN AMERICA, / 



also, seem to prevail, as in the mass of the same period in England, there being 

 at least five species among the few specimens brought by Dr. Gibbon. 



The extent of this formation in Columbia vras not observed by Dr. Gibbon, 

 nor were any observations made as regards the dip of the strata, or its direction. 

 The labels accompanying the specimens stated that they were taken up in the 

 road between Popoyan and Bogota, chiefly between La Messa and Tocaima. 

 Specimens thus collected could scarcely be expected to be found perfect, and 

 it is to be regretted that these are not better characterized. Such as they are, 

 I have ventured to describe them, with a hope of drawing the attention of 

 some geologist v/ho may pass through that country and observe the deposit 

 with attention. The mineralogical character of the specimens are very uni- 

 form, consisting of a dark slate-coloured argillaceous carbonate of lime, occa- 

 sionally accompanied by crystallized sulphuret of iron. 



In these few imperfect specimens we have an illustration of the importance, 

 nay, the absolute necessity, of a knowledge of the geo-zoological characteristics 

 to establish the age of the masses after a certain period. Zoological evidence 

 is the unerring guide to designate the different epochs. The importance of 

 ■this is established in a paper on the Age of the Limestones of South Devon, 

 recently read by Mr. Lonsdale before the Geological Society of London. In 

 this paper we are informed that Captain Smee and Captain Grant had recently 

 brought to England, from Cutch, and the desert east of it, suites of fossils from 

 " a series of beds unquestionably of the age of the Oolites of England, the fos- 

 sils agreeing, in their general characters, with those of that geological epoch" 

 in that country, and "being, in many instances, specifically undistinguishable;*' 

 thus establishing the fact of the deposits of the Oolitic period being immensely 

 extended, and proving, with the specimens now produced, that the unity of the 

 zoological existence of that period extended nearly, if not entirely round the 

 globe.* 



In Dr. Troost's Fifth Geological Report to the Legislature of Tennessee 

 (p. 6) he mentions a limestone of "an Oolitic structure" as existing near the 

 Cumberland Mountains. He states that the Oolite of the English geologists 

 is of " a more recent group," and that his Oolitic limestone is invariably found 



* Professor Vanuxem informed me recently that he picked up, some years since, a fossil Trigonia near 

 the ruin of a building in the city of Mexico. It had evidently been part of the structure, and probably car- 

 ried from some distance, as the rock over vi?hich the city is built is entirely volcanic. 



