Humberside Geologist no 16

(published 2019)

The Geology and Lichens of Saint Michael’s Church, Garton, East Yorkshire.

By Mark Seaward and Mike Horne.

St Michael's Church, Garton

St Michael’s church in Holderness  (NGR TA271355) can be found between Garton and Grimston and is about a kilometre from the sea. It is mostly built of erratic boulders probably collected from the fields or the beach. The stonework on the corners of the building is probably a Jurassic oolitic limestone and the buttresses on the south of the building are probably Magnesian Limestone. There is a porch built from medieval bricks which were probably made locally. This provides a wide variety of rock substrates for lichen.

Geology -

Here is a description of some of the erratic rocks that can be seen on the outside of the Church, if you wander in an anticlockwise direction starting at the porch:

South side – ironstone, basalt, Middle Jurassic sandstone, red chalk, Gryphaea, grey mudrock (weathering badly), quartzite and lichens were seen on a buttress of dressed Magnesian Limestone

limestone with lichen

East end – Old Red Sandstone (Devonian), New Red Sandstone (Peron-Triassic), cross-bedded grey sandstone and Magnesian Limestone

sandstone with lichen

North Side – vesicular basalt, locally made brick, pink granite, red sandstone, dolerite, bioturbated sandstone, Brockram, grey flint (Yorkshire flint from the Chalk), Larvikite (from Larvik in Norway), pink gneiss,  grey gneiss and Jurassic oolite (dressed stone making the surround to the north doorway)

red sandstone with lichen

West wall of tower- porphyry, corals in grey limestone, Gryphaea in shelly Jurassic limestone, grey sandstone (ganister?) and small pectenids and oysters in limestone

South wall of tower and west side of the porch – large Pecten in Jurassic ironstone, Chalk, septarian nodule, grey granite, New Red Sandstone, cross bedded Middle Jurassic sandstone and Carboniferous grey gritstone.

Inside the church – there is an  old altar of pale red sandstone.

The graves in the churchyard are mostly “York Stone” (Middle and Upper Carboniferous sandstones from the West Riding). There are some more modern monuments including the following stones -  Larvikite, coarse grained grey granite, medium grained grey granite, red sandstone and  Carrara Marble (from Italy).

The perimeter wall of the churchyard includes a variety of erratics including Chalk and is capped by brickwork.

church wall

The descriptions of the rocks are mostly generic and made from a quick visual inspection. No chemical tests were made and no samples taken.

Lichenology -

This basic survey demonstrated the value of lichens in environmental monitoring, on this occasion highlighting their preferences for particular substrata and the impact of over-riding factors such as the spread of nitrogenous compounds. Although relatively close to the sea, maritime effects on the lichen flora were hardly noticeable. The N, S, E and W walls of the church supported different lichen assemblages; however, the vertical gravestones generally lacked differences in the lichen assemblages on the E and W faces as would be expected, but their apices occasionally supported ornithocoprophilous lichens. Of the 43 lichen species recorded above only 35 were found on the stonework (7 were on trees, 1 was on a metal gate, and 1 on a pebbled pathway). The church and gravestones supported 21 and 25 species respectively and, in the case of the latter, 14 were found on siliceous substrata and 11 on calcareous substrata. There are no unusual or uncommon species on the list but time did not permit for a thorough investigation that would most probably double the number of species in the tally and may include some locally uncommon species.

In the following list, the numbers after each entry refer to the number of 10 km x 10 km grid squares (max. 195) in which the species occurs in Yorkshire, followed by the number (in parentheses) from which it has disappeared; thus Lecanora chlarotera, for example, occurs in 116 squares, has disappeared from 11, and has never been recorded from 68. The level of extinction, of considerable importance to conservation studies, can therefore be determined from these figures, but for many species our knowledge is imperfect due to taxonomic misapplication in the past or recent taxonomic segregation demanding reinterpretation of records for which limited herbarium material exists.


Substrates and habitats studied:


B – brick wall to W of churchyard

C – church (N, S, E & W walls mentioned where significant)

GC – calcareous gravestones

GS – siliceous gravestones

M – iron gate

P – compacted soil on pebbled pathway

T – deciduous trees to N of churchyard

[N] – nitrophytes


Acarospora fuscata (Schrad.) Th.Fr.   185(0)  GS

Amandinea punctata (Hoffm.) Coppins & Scheid.   141(3)  T

Aspicilia calcarea (L.) Körb.   120(3)  C & GC

Bilimbia sabuletorum (Schreb.) Arnold   111(3)  C (N wall – on mosses)

Buellia  aethalea (Ach.) Th.Fr.   118(0)  GS

Caloplaca aurantia (Pers.) Hellb.   50(7)  C (S & E walls) & horizontal cementwork of a single grave

C. chrysodeta (Vain. ex Räsänen) Dombr.  50(0)  C  

C. citrina (Hoffm.) Th.Fr.  []   194(1)  C & GC

C. flavescens (Huds.) J.R.Laundon   156(1)  C & GC

C. flavocitrina (Nyl.) H.Olivier   49(0)  C (calcareous stonework only) & GC

C. saxicola (Hoffm.) Nordin   131(5)  C (calcareous stonework only)

C. teicholyta (Ach.) J.Steiner   70(0)  C (calcareous stonework only)

Candelariella vitellina (Hoffm.) Müll.Arg.   192(1)  GS  [N]

Collema tenax (Sw.) Ach. var. var. ceranoides (Borrer) Degel.   41(5)  P

Diploicia canescens (Dicks.) A.Massal.   117(9)  C (S wall) & T [N]

Haematomma ochroleucum (Neck.) J.R.Laundon var. ochroleucum   80(1)  GS

Lecanora albescens (Hoffm.) Branth & Rostr.   172(3)  C & GC

L. campestris (Schaer.) Hue   167(1)  C & GS

L. chlarotera Nyl.   116(11)  T

L. crenulata Hook.   108(6)  C

L. dispersa (Pers.) Sommerf.   194(0)  C & GC

L. expallens Ach.   143(2)  GS & T 

L. muralis (Schreb.) Rabenh.   183(0)  GS (relaid horizontally)

L. orosthea (Ach.) Ach.   121(0)  GS

L. polytropa (Hoffm.) Rabenh.   190(0)  GS

L. soralifera (Suza) Räsänen   165(0)  GS

Lecidella elaeochroma (Ach.) M.Choisy   81(13)  T

L. scabra (Taylor) Hertel & Leuckert   175(0)  GS

L. stigmatea (Ach.) Hertel & Leuckert   172(1)  GC

Lepraria incana (L.) Ach.  []  194(0)  C (N wall) & GS   

Opegrapha calcarea Turner ex Sm.   79(7)  C (N wall)

Phaeophyscia orbicularis (Neck.) Moberg   184(0)  T

Physcia adscendens (Fr.) H.Olivier   180(1)  GC, M & T [N]

P. tenella (Scop.) DC.   164(4)  T

Porpidia tuberculosa (Sm.) Hertel & Knoph   183(0)  C & GS

Psilolechia lucida (Ach.) M.Choisy   181(0)  GS

Sarcogyne regularis Körb.    115(3)  C

Tephromela atra (Huds.) Hafellner ex Kalb   136(8)  C & B

Toninia aromatica (Sm.) A.Massal.   105(7)  B (cementwork between bricks)

Verrucaria muralis Ach.   177(2)  C & GC

V. nigrescens Pers.   181(0)  C & GC

Xanthoria parietina (L.) Th.Fr.   188(1)   T [N]

X. polycarpa (Hoffm.) Th.Fr. ex Rieber   122(3)  M [N]

 Acknowledgments -

These notes were compiled with the help of Stuart Jones on a field trip of the Hull Geological Society to record the lichen and geology on 22nd April 2017. We thank Lif Marriott and Paul Fisher for facilitating our visit.


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copyright Hull Geological Society 2019