28 . ANNUAL ADDRESS, MDCCCLXXIII. 



port of this quantity it would require a fleet of 2,000 

 Indiamen, each of 1,400 tons, to start every day through- 

 out the year. Such a mass of matter would cover a 

 square space fifteen miles in the side every year with mud 

 a foot deep, or would raise the whole surface of Ireland 

 one foot in 144 years. The Mississippi, according to the 

 measurements of Messrs. Humphreys and Abbott, conveys 

 every day into the Gulf of Mexico 53,424,657,534 cubic 

 feet of sediment." These deposits, by the cementing power 

 of oxide of iron, silica, great and long-continued pressure, 

 accompanied sometimes by heat, have become hardened 

 into rocks of various degrees of consistency, and in the case 

 of the Pennine chain, now that the sea has been driven 

 back, and the strata upheaved by subterranean force or 

 lateral shrinkage, form the grand and rugged backbone of 

 the northern half of England. 



But it is not on this description of rock that I would 

 further dwell, but on that other class which is represented 

 by the vast accumulation of what is called limestone, an 

 inquiry into which is the object of my address, with a 

 view to consider and examine those methods by which it is 

 said to have been formed into its present condition. 



First, permit me to describe to you to what geologic 

 epochs the various limestones belong, with passing reference 

 also to the physical geology and geography of this most 

 interesting substance. Limestone of one kind or other is 

 a constant corollary to each geological formation and epoch. 

 It is consequently found in the oldest rocks which show 

 any signs of stratification. The most ancient rocks in 

 which we have evidence of stratification are the Laurentian 

 group, so called from the Canadian geological surveyors 

 having found, northwards of the river St. Lawrence, "a 



