PRINCIPLES OF GEOLOGY. 7 



above important proposition. And though we only refer to a particular 

 district, yet, without doubt, any part of the world, where the strata are 

 distinctly visible, would equally illustrate the doctrine of local constancy 

 in the order of succession among rocks ; because in every country this 

 conclusion has been drawn from actual observations. But it may be 

 inquired : How can the strata be thus traced across provinces and king- 

 doms ? we see them, indeed, exposed on the sea-coast, but how are we 

 to guide our inquiries inland, when wells and pits fail us ? I answer, that 

 as the different rocks lie not quite horizontal, but gently sloping into the 

 interior, the surface of the earth is formed on their edges. Thus, com- 

 pare the accompanying geological map and section, and observe in the 

 section the chalk rising uninterruptedly from Bridlington to Speeton, 

 when, another stratum, the blue clay, having risen from beneath it to 

 the surface, that rock passes off inland, and keeps a regular course 

 through the country. In the same manner, the calcareous grit rises from 

 the sea at Filey, ascends to the summits of Gristhorpe and Red cliffs, 

 afterwards attains the height of Oliver's mount, and ranges away in a 

 direction parallel to the chalk. The same is the case with all the other 

 strata, represented by the colours on the map. Thus, the surface of the 

 earth is formed on the edges of the strata, a wise and admirable pro- 

 vision, whereby mankind, though till lately regardless of the benefit, are 

 provided with so great a variety of mineral matter, suited to the various 

 and increasing wants of civilized life. To trace the rocks through the in- 

 terior of a country, demands, it must be confessed, greater diligence and 

 caution, than when we see them exposed on the sea-side ; but the result, 

 thus prudently obtained, may be as absolutely trusted. Nor are facilities 

 wanting to the practised inquirer. To him, the forms of hills, the cha- 

 racter of surface, the very herbage and colour of the soil, afford most 

 valuable data, and when corrected by the accounts of wells and pits, 

 and observations of roads and water-courses, leave little room to doubt 

 the accuracy of his deductions. 



This being proved, we may now inquire if there be a conformity of 

 rocks over large districts, an accordance of composition, a similarity of 

 succession, and a connexion of strata, sufficient to unite together obser- 



