Ordnance survey of the county of Londonderry / Colonel Colby ... superintendent. Volume the first.
- Ordnance Survey of Ireland
- Date:
- 1837
Licence: Public Domain Mark
Credit: Ordnance survey of the county of Londonderry / Colonel Colby ... superintendent. Volume the first. Source: Wellcome Collection.
23/414 (page 3)
![NATURAL FEATURES. On the 19th of January, 1692, a frost commenced, which continued with great severity for five weeks. In the “ Annals of Derry,” by Mr. Gillespie, two other remarkable frosts are recorded. The first wras that of 1739-40, commonly called throughout Ireland “the year of the hard frost”—a fami- liar epoch with the lower orders: during this frost the river Foyle was frozen over, and an ox was roasted on the ice, opposite to the Ship Quay. The other was in 1814, when the ice on the river was so strong that carriages were driven over it in several places, and—on the 6th of February—a part of the bridge was carried away by masses of ice, floated down the river by the ebb tides and a very high wind. And, when it is recollected that such unusual and impressive events are more likely to dwell on the memory than the more simple and unobtrusive fact of a peculiarly mild and genial season, it may be reasonably doubted whether the change alluded to is more than a periodical return of warm seasons, alternating with others of severe and rigorous cold. Dr. Patterson, also, records a remarkable frost, that occurred in 1802, from which, after only six days of uninterrupted freezing, the Foyle, where it is above 1000 feet broad, was covered with ice. The thaw was succeeded by a tremendous storm, which did considerable damage in Derry, and its neighbourhood. A large stone, at the summit of the former spire of the cathedral, was displaced by the vibration of the spindle that supported the vane, by which the spire was surmounted; and a large sheet of lead was whirled from one of the valleys in the roof of the Presbyterian Meeting- House, and carried by the wind over a back-yard into another adjoining it. Ten days after this hurricane there was a very violent gale. There are similar instances of hard frost, and other variations of weather, recorded in the earlier annals of the district, which, however, are not so immediately connected with the parish as to claim notice here. In 1146, and 1178, violent storms occurred, which did considerable damage at Derry. [See General History.] The most remarkable circumstance bearing on the subject of Climate was a meteoric appearance, which occurred at the time of the death of bishop Murry O’Coffy, in 1173. [See Do.'] NATURAL HISTORY. Geology A geological description, founded on the principles of practical utility, naturally divides itself into two sections:—1. Rocks (including clays, sands, &c.), as regards their mutual rela- tions in geological science ; 2. Rocks (&c.), as regards their application to practical purposes. And the first of these sections may be again divided into two sub-sections, namely:— 1. Rocks in situ (including stratified clays and sands)—Being a consideration of the order of their geological position, and of the accidents which have affected or modified their arrangement. 2. Detritus—Being a consideration of those accumulated fragments, which now form beds of clay, sand, or gravel, and have proceeded from the disintegration, removal, and re-arrangement of those pre-existing rocks, which are now recognized as part of the visible crust of the Earth. Section 1.—Sub-section 1.—Rocks, fyc., in situ. The geological structure of the parish is simple; and it may be observed that it has no exact geological boundary—the same rocks occurring on the opposite side of the Foyle, and on the W. and N. of the parish, in the county of Donegal. The great mass of the primary schistose rocks, which occupies so much of the western part of the county, spreads over its whole surface, with the exception of a considerable detritic patch at Culmore, in the N. E. of the parish—which probably conceals a part of the new red sandstone, that rock being visible at the extreme northern end of the parish—and of several very limited deposits of mud and clay, which, on the S. E., skirt the river Foyle. Within this space the rocks exhibit a considerable variety of texture, passing through several steps of progres- sion from a rough and knotty pseudo-gneiss into a smooth, even, and apparently homogeneous slate. That these varieties have a definite and regular order of arrangement is improbable, although it does appear that some of them recur frequently with the same characters, and are sufficiently persistent over a large extent of country to be admitted as types of the following subdivisions: — 1. Mica Slate, passing into Gneiss. G. m. s Specific Gravity—2.65. 2. Mica Slate, passing into Clay Slate. G. m. c Do. —2.84. 3. Mica Slate, passing into Quartz Slate. G. m. q. .- Do. —2.69. The dip varies in direction from N. to N. W., and in amount from 30° to 55°; but here, as in all the primary slates, much doubt and difficulty must attend the determination of the dip, and the very fact of distinct stratification is sometimes questionable. The laminae of these schists are usually b 2](https://iiif.wellcomecollection.org/image/b2200709x_0023.jp2/full/800%2C/0/default.jpg)
