<;KOLOGICAL KECOIJD. 97 



which are brought down by their waters in a state of suspension, 

 forming what are called " Deltas." 



From the observed uniformity of Nature's laws and workings, it 

 is reasonable to infer, therefore, that a cause constantly operating in 

 this way at the present time in the case of the above-named and 

 other rivers, has also been operating in the same way from remote 

 antiquity. In the course of these formations, multitudes of plants, 

 including even large trees, have been embedded in the soft deposits 

 of silt and mud, and their remains preserved in the rock which 

 results from the hardening of the mud. The soft and delicate parts 

 could not be perpetuated in this manner, and it is found, in fact, 

 that only the harder parts, such as the wood, bark and fruits are 

 preserved. The softer portions have been more or less quickly 

 decomposed, although under especially favourable conditions there has 

 been some preservation even of these ; they have in some instances 

 left impressions in the hardening mud, and from which the form and 

 even the species can sometimes be recognised. 



Geologists have classified the different beds or strata composing the 

 Earth's crust into five main divisions, and these divisions are further 

 divided into systems, the systems into series, sections or formations, and 

 these again into groups and stages ; each group or stage includes 

 two or more zones or horizons which may consist of one or several 

 beds or strata. To all these divisions and sub -divisions they have 

 given technical names. They have also assigned to them a -chrono- 

 logical order of formation, not indeed by referring them to a 

 particular year or number of years reckoned from a fixed epoch, 

 but from an examination of the fossil remains and from other data 

 they have ascertained which strata are of earlier formation and which 

 are more recent. The entire series of beds or strata so classified 

 and chronologically arranged forms the Geological Record. 



u The Geological Record is at the best but an imperfect chronicle 

 of the geological history of the Earth. It abounds in gaps, some of 

 which have been caused by the destruction of strata owing to 

 metamorphism, denudation or otherwise. Nevertheless, it is from this 

 record that the progress of the Earth is chiefly traced. It contains 

 the registers of the births and deaths of tribes of plants and animals 

 which have from time to time lived on the Earth. Probably only a 

 small proportion of the total number of species which have appeared 

 in past time have been thus chronicled, yet by collecting the broken 

 fragments of the record, an outline at least of the history of life 

 upon the Earth can be deciphered."* 



* Text Book of Geology, by Sir Archibald Geikie, p. 634. " Upon the leaves of that 

 stone book are stamped the characters plainer and surer than those formed by the ink of 

 history, and which carry the mind back into the abysses of past time, compared with 

 which the. periods which satisfy the unscientific mind cease to have a visual angle. "- 

 Di\ John Tfi,,(l<iJl. ; tlif Belfast Address. 



