MINE. 



319 



p.,-- .. 



Mine* of that the dip of the strata from H to C is much greater 



Coal. t han the dip from I to C, so that while the coals from 



v i ~ 1 " C to I are flat, having a moderate rise, the coals from 



C to H have a great rise, and are frequently of the class 



of edge coals. A right understanding of these plans and 



sections will make the other figures of a coal-field and 



segments of the bason more easily comprehended. 



The next form or shape of a coal-field is that which 

 is semi-elliptical, as represented by the horizontal sec- 

 Pt*ra tion, Fig. 5. where A and B are coals with their ac- 

 COOUUTIII. companying strata, having their line of bearing in the 

 ^fr i- direction C, D, and the line of dip from E to F, these 

 coals are cut off in the line of dip by a natural figure 

 in the strata C, D ; hence, in prosecuting the working 

 of the coals to the dip they are lost, and in place of 

 coal, nothing but stone, or the strata accompanying coal, 

 are to be found : the nature of this fissure or obstruc- 

 tion will be explained afterwards. 



These forms of coal-fields now described, or modi- 

 fications of these forms, are what we find the most com- 

 mon. There are, however, instance* of the inverted 

 bason form, and of inverted segments of it ; but these 

 are very rare in comparison with the other. Fig. 6. is 

 the vertical section of this form, A, B, C, represent the 

 coals dipping in every direction to F and G. 



The cover of earth which lies above the strata i* of 

 earth above two distinct kinds, both of which are alluvial, the one 

 the racks. )<]. tnan tne other, viz. 



1 . The recent alluvial cover. 



2. The old alluvial cover. 



The recent alluvial cover is found by the sides of 

 rivers and arms of the sea, in general very little ele- 

 vated above the surface of the water* which evidently 

 formed them. 



The old alluvial cover succeeds the recent alluvial cover, 

 is in general more elevated, and extends to the top* of 

 the mountains ; there, however, it is found very thin. 

 It is in the intermediate moderately rising ground 

 where it is found of the greatest depth. 



The recent alluvial cover we have found to be in some 

 instances nearly 100 feet, and the old alluvial 180 feet 

 in depth, above the rock. 



The recent alluvial cover is generally composed of soil, 

 clay, wet sandy loam, sludge, and sometimes beds of 

 peat earth, also bed* of gravel ; and in digging through 

 it, trunk* of large tree* and brushwood are frequently 

 found, with beds of sand containing great varieties of 

 sea shells ; adjoining the arms of the sea, the remains of 

 marine animals from the largest to the smallest size are 

 also occasionally found. In the alluvial cover, by the 

 sides of quick running rivers in coal districts, piece* 

 of coal and of the accompanying strata abound, but 

 adjoining slow running rivers and arms of the sea, 

 these fragments are seldom to be found, excepting when 

 brought there accidentally. 



The old alluvial cover is commonly composed of clay 

 intimately mixed with sand, small rounded stones, and 

 frequently with boulder stones, from a few pounds to 

 several tons in weight ; it is quite impervious to water, 

 and is termed till by agriculturist'. In examining this 

 cover when broken up, it is found to contain fragments 

 of almost all the strata of the adjoining coal-field, such 

 as sandstones, slate-clay, ironstones, and coal, the 

 largest only a few inches in size, the angles sharp, 

 which shew they had not suffered by attrition. It is re- 

 markable that no remains of trees or plants are to be 

 found in this earth, nor any remains of marine animals 

 or shells, though immediately adjoining the recent al- 

 luvial soil where they are so abundant. This cover has 



)MI1I CO- 



OU alluvial 



sometimes beds of sand in it, and at the foot of moun- Mines of 

 tains is mixed with many fragments of the mountain ^ < ? al ' .. 

 rocks. -"V 1 



As to the general situation of coal-fields with their Situation 

 accompanying strata, they are found, ofcoal- 



1. Under the level of the sea. 



2. Above the level of the sea, moderately elevated. 



3. Considerably elevated above the level of the sea. 

 Having considered the shape or form of coal-fields as 



uniform and entire, we have now to describe the dis- 

 locations and ruptures of the strata, for it is found in 

 practice, that in place of a regular figure, the bason 

 form is broken, dislocated, and deranged, forming seg- 

 ments of every various form, the dislocations, extend- 

 ing from a quarter of an inch to upwards of (iOO feet, 

 in a perpendicular or sloping direction, or separated 

 horizontally from the breadth of an inch to upwards 

 of 100 feet: It is these dislocations which render the 

 searching for coal, and the operations connected with 

 the working of it, so difficult and intricate, while at the 

 same time they are frequently of the greatest benefit. 



The dislocations and obstructions which are found Dislocation 

 in coal-fields, are known by the names of of the 



1. Dikes. " riw - 



t. Slip. 



3. Hitches. 



4. Troubles. 



The three first relate to the dislocation of the strata, 

 the fourth, or what is termed troubles, relates to the 

 changes which take place in the bed of coal. 



A dike is like a wall of extraneous matter, which Dike*, 

 divides all the beds of coal found in a coal-field. It 

 varies from a few inches to many fathoms in thickness, 

 and penetrates through the strata to the greatest depth 

 the miners' operations have yet reached ; they are com- 

 posed of, 



1. Sandstone. 



2. Greenstone. 



3. Basalt. 



4. Porphyritic clay mixed with white calcareous 

 spar. 



5. Heterogeneous mixture of the coal strata. 



6. Water gravel. 



7. Quicksand. 



8. Old alluvial clay. 



9. Recent alluvial clay. 



The first five in the order may more properly be 

 nsrtd dikes. The four last are more commonly 

 known by tin- name of gaws, gashes, or chasms. 



A slip is a fissure in the etrata, from the tenth of an Slip*, 

 inch to two or three feet in width ; which fissure is 

 filled with rubbish and fragments of all the strata found 

 in the coal-field. The strata, on one side, arc slipped 

 past those on the other side of the fissure, and this ili-- 

 tocation receives the name of a slip, where the coal has 

 slipped off its parallelism fully its own height. These 

 lip* are found from the extent of a few feet, to up- 

 wards of 600 feet perpendicular. 



A hitch i* a smaller kind of slip, where the disloca- Hitchn. 

 tion is from an inch to the extent of the thickness of 

 the coal. In some mining districts, slips and hitches 

 are known by the very appropriate name of steps. 



Troubles affect the stratum, or bed of coal, not only Troubles, 

 as rendering it very difficult to work, but very inferior 

 in quality, and frequently altogether useless a* an ar. 

 tide of commerce. These troubles are not found in 

 the chief extent of a coal-field, they only affect it par- 

 tially, and may be classed under the following 



